# HL Chemistry 3 The course code for this page is **SNC4MZ**. ## Organic chemistry !!! definition - An **organic molecule** is one with at least one carbon atom covalently bonded to another carbon or hydrogen atom (i.e., at least one C-H or C to C bond) Carbon is unique in organic chemistry as it is the only element with the following properties: - It is in the second row of the periodic table, meaning it has less electron shells, thus forming stronger bonds - It can covalently bond to up to 4 other atoms - Because each of its valence electrons is involved in bonding, it can form single through triple bonds - The molecular geometry can be anything from tetrahedral to linear depending on its bonding Carbon is also able to bond to itself in the following ways: - long straight chains - long straight chains with branches - rings (Source: Kognity) ### Simple hydrocarbons !!! definition - A **branched hydrocarbon** is one with at least one "side group" extending from the main hydrocarbon chain. - A **functional group** is a group of atoms responsible for the characteristic properties of a molecule (e.g. C=C) - A **homologous series** is a family of organic compounds with the same functional group but the hydrocarbon chain length changes by 1 $\ce{CH2}$ group. These only contain carbon and hydrogen. **Alkanes** are a homologous series that only contain single bonds between carbons, and are named with the number of carbons with the suffix "-ane". (Source: Kognity) | Carbon atoms | Prefix | | --- | --- | | 1 | Meth | | 2 | Eth | | 3 | Prop | | 4 | But | | 5 | Pent | | 6 | Hex | | 7 | Hept | | 8 | Oct | | 9 | Non | | 10 | Dec | !!! example A molecule with only hydrogen and three carbon atoms all held together with single covalent bonds is called "propane". **Alkenes** contain **at least** one carbon-carbon double bond and are named with a prefix with the total number of carbon atoms and "-ene". **Alkynes** contain **at least** one carbon-carbon triple bond and are named with a prefix with the total number of carbon atoms and "-ene". !!! warning The lack of standardisation prior to IUPAC means that some IUPAC names have common names that are still widely used today. - acetylene: **ethyne** - vinyl / ethylene: **ethene** The general formula for an **acyclic** hydrocarbon with no rings is as follows, where $n$ is the number of carbon atoms, $x$ is the number of double bonds, and $y$ is the number of triple bonds. $$\ce{C_nH_{2n+2-2x-4y}}$$ ### Representing organic compounds A simple **molecular formula** is the least useful as it provides no information on structure and bonding. $$\ce{C6H14}$$ A **complete structural diagram** shows all atoms by their chemical symbols and uses lines like a Lewis Dot diagram to represent bonds. VSEPR shapes do not need to be taken into account because these are 2D representations of the molecule. A **condensed structural diagram** is a complete structural diagram but C-H bonds are aggregated into a formula. $$\ce{CH3 - CH2 - CH2 - CH2 - CH2 - CH3}$$ A **structural formula** or **expanded molecular formula** is a condensed structural diagram but there are no bond lines. The bond organisation is inferred based on the number of hydrogens on each carbon. Carbon chain side groups (branches) are shown with parentheses. $$\ce{CH3CH2CH2CH2CH2CH3}$$ A **condensed structural formula** is a structural formula but any consecutive repeated $\ce{CH2}$ groups are factored with parentheses. $$\ce{CH3(CH2)_4CH3}$$ A **line diagram** or **skeletal structural formula** removes carbons and hydrogens and replaces all carbon-carbon bonds with lines, where the number of lines represents the type of bond. Each line is bent where a carbon atom would be, except for triple bonds as those are linear. Non-carbon groups such as $\ce{OH}$ can be shown in collapsed form. !!! example These are the ways to represent pentane, $\ce{C5H12}$. The structural formula is mislabeled as a condensed structural diagram. (Source: Kognity) ### General nomenclature To name an organic compound: 1. Find the **longest acyclic chain** of carbon atoms as the parent chain. 2. Assign numbers from 1 to $n$ for each carbon atom in the parent chain. - The numbers should be arranged in a way that the highest priority functional group in the chain is assigned the lowest number possible. - Apply the **first branch rule** only if there is a tie: If there are side chains, the parent chain should be numbered such that the location of any side chains have the lowest number possible. - If there is a tie, the location with the most branches wins. - If there is a tie, the rest of the chain is compared in sequence applying the first branch rule. - If there is a tie, the first location with the side chain group name that is alphabetically greater wins. - If there is a tie, it doesn't matter which side is picked as the whole thing is symmetrical. 3. Name the main chain based on the name of the functional group and location number for the functional group in the format "number-name". 4. Name the side groups. - If the group is not carbon, name it by its identity. - Otherwise, name the hydrocarbon based on the number of carbons in the side group with the ending "yl". - If there is more than one identical side group in the **whole chain**, combine their numbers and names with a Greek prefix. - Assign a number representing the carbon atom of the parent chain that the side group is attached to in the form "numbers-name". 5. Arrange the name with each side group with their numbers in alphabetical order, discounting any prefixes due to duplicates, followed by the parent chain. 6. Join everything together: - Drop the ending vowel from the prefix if there is a double vowel unless it is "i". - Separate numbers from words with dashes. - Separate numbers from numbers with commas. - Do not separate words from words. !!! tip In hydrocarbons: - Atoms with double or triple bonds share equal priority as the highest functional group. - The main chain will be named as an alkane if there are only single bonds. - If there is exactly one double or triple bond, it will be named as an alkene or alkyne with its position inserted between the prefix and ending. - e.g., "pentane", "pent-2-ene" - If there are multiple double or triple bonds, their numbers are also included, but an "a" is appended to the prefix and a Greek prefix added to the suffix. - e.g., "penta-1,3-diene", "hexa-1,3,5-triyne" - If there are both double and triple bonds, the "-ene" becomes "-en" and is always before "-yne". - e.g., "pent-4-en-2-yne" !!! example tf Other **side chains** with equal priority as double or triple bonds *in side chains* include: - halogens, which have their "-ine" suffix replaced with "o" (e.g., "chloro") - $\ce{NO2}$: "nitro-" - benzene (as a side chain): "phenyl" If there is no other option and there is a **branched side chain**, name it based on the total number of carbon atoms in the side chain. !!! example tf ### Cyclic aliphatic hydrocarbons These contain rings that **are not** benzene rings. $$\ce{C_nH_{2n-2x}}$$ !!! warning Cyclic hydrocarbons **do not** contain any triple bonds as it would force the carbon ring to widen too much. Cyclic aliphatic hydrocarbons are named the same way as acyclic hydrocarbons except they have a "**cyclo-**" at the start of the name of their parent chain. !!! example cyclohexa-1,3-diene The initial double bond should be numbered such that the lowest number is assigned to both sides of the bond (numbers 1 and 2 should be to either side of the double bond). If there is more than one double bond, the ring should be numbered such that the lowest number is assigned to both. The **first branch rule** still applies. (See [HL Chemistry 3#General nomenclature](/snc4mz/#general-nomenclature).) !!! example tf !!! warning Rings can be side chains, and are named accordingly (e.g., "cyclopropyl"). The "cyclo-" prefix is counted when sorting names alphabetically as it describes the group. ### Cyclic aromatic hydrocarbons These contain benzene rings, which do not actually have single/double bonds as they actually have delocalised pi bonds. (Source: Kognity) As benzene rings do not have double bonds, they are named according to the **first branch rule**. ### Isomers **Structural isomers** are two chemicals that have the same chemical formulas but have different structural formulas, resulting in different chemical properties. **Hydrocarbon chain isomers** are two chemicals with the same chemical formulas but have different carbon/hydrogen arrangements. !!! example The following are two hydrocarbon chain isomers (and, by extension, structural isomers) of $\ce{C5H12}$. (Source: Kognity) **Positional isomers** are two chemicals with the same chemical formulas **and functional groups** but have different structural formulas. !!! example The following are positional isomers (and, by extension, structural isomers) of $\ce{C4H8}$. (Source: Kognity) **Functional group isomers** are chemicals with the same chemical formulas but **different functional groups**. !!! example The following are functional group isomers (and, by extension, structural isomers) of $\ce{C3H6O2}$. (Source: Kognity) **Geometric** or **cis/trans isomers** are two chemicals have the same chemical formulas and atom arrangements but are positioned differently, thus having ambiguous names. In order for this to occur, there must be two different atoms or groups of atoms bonded to each carbon atom in the double bond. - A **cis** hydrocarbon isomer will have its main chain enter and exit the double bond on the **same side**. - A **trans** hydrocarbon isomer will have its main chain enter and exit the double bond on **opposite sides**. Unlike the examples below, these should be named with "cis" or "trans" at the beginning as a **separate word without a hyphen**. !!! example The following are two geometric isomers of but-2-ene: (Source: Kognity) - In acyclic compounds, this is because the double bond prevents simply rotating one side but not the other as it would force breaking the pi bond. - In cyclic compounds, this is because the ring's other side is similar to a double bond, preventing rotation around the axis. !!! example The following are cis-trans isomers of dichlorocyclobutane (notice the chlorine): (Source: Kognity) Isomers may have different physical properties in: - **polarity**: a cis isomer may cause a molecule to be polar as opposed to its trans variant - **packing efficiency**: a non-branching hydrocarbon chain will pack better than a branching one, and a continuously trans chain will pack better than a cis one These change the strength and type of intermolecular forces involved so affect their melting/boiling points. Isomers may also have different chemical properties as cis isomers are more likely to bump into themselves to make some reactions more viable ### Benzene reactions !!! definition - An **electrophile** is any species that is or would be electron deficient (+) in the presence of a pi bond. In reactions involving a benzene ring, the ring itself is **stable** and will not break apart because of the strength of delocalised pi bonds. Therefore, only the hydrogens can be swapped out via **electrophilic substitution**, where an hydrogen atom is substituted with an electrophile. The concentration of electrons in the delocalised pi area attracts electrophiles to initiate the bond. In the mechanism diagram below, $\ce{E+}$ represents the electrophile. Curly arrows are used to show the movement of electrons from the **delocalised area to the electrophile** and **hydrogen atom to the delocalised area**. (Source: Kognity) The **first step** (the change from the first to the second diagram) is the **slow step** due to the highest activation energy due to the requirement to break a bond. (Source: Kognity) #### Benzene nitration !!! definition - A **nitrating mixture** is a mixture of concentrated sulfuric and nitric acids. In a **nitrating mixture**, benzene will react with positive nitronium ions at **~50°C** to form nitrobenzene, outlined in the reaction mechanism diagrams below. $$\ce{C6H6 + HNO3_{(aq)} ->[conc H2SO4][50^\circ C] C6H5NO2 + H2O_{(l)}}$$ (Source: Random Quora Person) The first step is to **form the nitronium ion** through a Bronsted-Lowry acid-base reaction between the acids. $$\ce{HNO3_{(aq)} + H2SO4_{(aq)} <=> H2NO3+_{(aq)} + HSO4-_{(aq)}}$$ The lone pair on the oxygen of the nitric acid attracts a hydrogen atom, which becomes an $\ce{H+}$ ion as sulfuric acid's oxygen takes its electrons. The hydrogen ion bonds to the nitric acid. $$\ce{H2NO3+_{(aq)} <=> H2O_{(l)} + NO2+_{(aq)}}$$ The oxygen-hydrogen group is conveniently able to form water by taking both electrons it was sharing with the nitrogen. The other single-bonded oxygen compensates with a dative covalent bond with the nitrogen to form the nitronium ion. The second step is to **react with benzene** through electrophilic substitution, with electrons moving back from the dative oxygen-nitrogen bond back to the oxygen. ### Alkane reactions !!! definition - **Halogenation** is the introduction of a halogen into a compound. #### Substitution halogenation Because a sigma bond must be broken, alkanes are not very reactive. In the presence of light, alkanes will react with halogens in their standard state through halogenation, replacing one of their hydrogens. **Fluorine** is an exception that does not require light because it is highly reactive. If the halogen is in excess and the reaction continues, more of the halogen (**not the hydrogen-halogen product**) will react with the alkane until all hydrogens have been substituted. !!! example $$\ce{CH3CH3 + Cl2_{(g)} ->[light] CH3CH2Cl + HCl_{(g)}}$$ If $\ce{Cl2}$ is in excess: $$ \ce{ CH3CH2Cl + Cl2_{(g)} ->[light] CH3CHCl2 + HCl_{(g)} \\ ... \\ CCl3CHCl + Cl2_{(g)} ->[light] CCl3CCl3 + HCl_{(g)} } $$ The order that hydrogens are substituted in is **random**. If there is more than one possibility, all of them are written as products, ignoring balancing. !!! example Propane reacts with chlorine gas to form either 1-chloropropane or 2-chloropropane. $$\ce{CH3CH2CH3 + Cl2 ->[hf] CH3CH2CH2Cl + CH3CHClCH3 + HCl}$$ !!! example 1-bromoethane reacts with chlorine gas to form either 1,1-dibromoethane (40% chance) or 1,2-dibromoethane (60% chance) because each hydrogen is equally likely to be substituted, and there are 2 and 3 that would form them, respectively. $$\ce{CH2ClCH3 + Cl2 ->[hf] CHCl2CH3 + CH2ClCH2Cl + HCl}$$ #### Free radical substitution !!! definition - A **free radical** is a species with a lone unpaired electron. - **Homolytic fission** is the dissociation of a chemical bond in a neutral molecule where each product takes one electron, generating two free radicals. - **Heterolytic fission** is the dissociation of a chemical bond in a neutral molecule where one product takes both electrons. The free radicals are first produced with the help of light energy. $$\ce{Br2 ->[hf] Br. + Br.}$$ They are then spread to organic compounds and reformed. $$ \ce{ Br. + CH4 -> .CH3 + HBr \\ Br2 + .CH3 -> CH3Br + Br. } $$ This cycle only ends when all radicals are used up, through reactions that end up with a net loss in radicals, such as: - $\ce{Br. + Br. -> Br2}$ (unlikely, contributes a little) - $\ce{.CH3 + Br. -> CH3Br}$ (likely) - $\ce{.CH3 + .CH3 -> CH3CH3}$ (likely) !!! warning The free radical is on the carbon atom, not the hydrogen atoms, so the marker goes at the beginning. ### Alkene/yne addition reactions !!! definition - A **carbocation** is a compound with a $\ce{C+}$ atom. - The **primary** (1°), **secondary** (2°), and **tertiary** (3°) carbocations are carbocations bonded to one, two, and three other carbon atoms, respectively. The presence of double/triple bonds make alkenes and alkynes more reactive and also allow the **addition** of species as pi bonds are easier to break. Addition always takes precedence over substitution when possible. These **spontaneous** reactions break the double/triple bond down a level and slot themselves in (i.e., alkynes form alkenes, alkenes form alkanes). $$ \ce{alkene + Br2 -> alkaneBr2} \\ \ce{alkyne + Br2 -> alkeneBr2} $$ (Source: Kognity) 1. If the non-alkene/yne reactant does not have a dipole moment, the electrons concentrated in the double/triple bond of the alkene/yne induce a dipole by repelling the electrons closest to it. 2. The positive dipole (such as H in HBr) is attracted to the double bond, and **two electrons** in the bond are used to form a **dative** bond with the positive dipole. 3. No longer needing its old bond, the previously positive dipole loses **both electrons** in its old bond to the negative dipole. 4. The now positive carbon atom attracts the now negative ion. 5. The negative ion forms a **dative** bond with the positive carbon atom. !!! warning - If an **alkene is formed**, the same randomness of where the atoms attach applies, so it is possible that a cis/trans isomer is formed. - If an **asymmetrical alkane** is formed, the same randomness of where the atoms attach applies after applying Markovnikov's rule, so it is possible that positional isomers are formed. **Markovnikov's rule** states that in Soviet Russia, the rich get richer. Hydrogens preferentially bond to the carbon with the **most hydrogens** if there is one — otherwise it randomly chooses one available. This is because carbocations with that are *more highly substituted* (are bonded to more carbon atoms) are more stable, so they last longer and are more likely to form a bond with the negative dipole. The preferred product is the **major product** while the other is the **minor product**. Some minor product will still be produced if the negative dipole is speedy enough, although it will be vastly outnumbered by the major product. #### Halogenation Unlike alkane substitution, addition halogenation is spontaneous. $$\ce{alkene + Br2 -> alkaneBr2}$$ !!! example This process is used to test for alkenes/alkynes in a solution. As bromine water is red-brown, if alkenes/alkynes are present, the water will be **decolourised** from red-brown to become more colourless. !!! example (Source: Kognity) #### Hydrogenation The addition of hydrogen follows the same principle as that of halogenation. $$\ce{alkene + H2 ->[\text{heat, high pressure, Ni/Pt/Pd}] alkane}$$ !!! example (Source: Kognity) #### Hydrohalogenation The addition of both a hydrogen and halogen follows similar principles. $$\ce{alkene + HBr -> alkaneBr}$$ #### Hydration Hydration is the addition of an $\ce{H-OH}$ group (colloquially known as water) onto an alkene/yne within 6 mol/L $\ce{H+}$ to produce an alcohol. $$\ce{alkene + H2O ->[6 mol/L H+] alkaneOH}$$ !!! example (Source: Kognity) ### Nucleophilic substitution !!! definition - A **nucleophile** is a species with a lone pair or a negative charge. Nucleophilic substitution replaces a group of atoms attached to a C with a nucleophile. Both processes involve the **leaving group** taking both electrons, becoming negative in the process, and forming a carbocation as the other product, which attracts and bonds with the nucleophile. Effectively all reactions here involve the formation or stealing of dative covalent bonds. Where $\ce{X}$ is a halogen: $$\ce{R-X_{(l)} + OH-_{(aq)} -> R-OH_{(aq)} + X-_{(aq)}}$$ If substituting with hydroxide, it must be **warm** and **aqueous** (dilute). Generally: | Carbocation type | Substitution type | | --- | --- | | Primary | SN2 | | Secondary | Both/either | | Tertiary | SN1 | #### SN1 This **two-step** reaction involves the heterolytic fission of the C-X bond to form a carbocation + halide ion (slow), followed by the nucleophile's lone pairs/negative charge attracting it to the carbocation. The "1" refers to the order of the rate-limiting step being a **unimolecular** collision. (Source: Kognity) !!! warning Be sure to draw VSEPR, unlike in the diagrams above. #### SN2 This **single-step** reaction has the nucleophile forming a bond with the central atom **opposite the leaving group** in a "back-side attack". The oncoming nucleophile repels the other groups, causing them to move away, effectively **reflecting** ("inverting") the remaining groups across the vertical axis. The "2" refers to the order of the rate-limiting step being a **bimolecular** collision. (Source: Kognity) !!! warning Dashes must be drawn for the transition state for bonds breaking/forming. In this case, drawing the front/back lines for the bottom two atoms may be ignored in favour of regular lines instead to avoid the ambiguity of forming bonds. #### Factors affecting substitution type **Steric hindrance** is the effect of other parts of a molecule getting in the way to the central atom, preventing a reaction. If there is not enough space for a backside attack, SN2 cannot happen. Therefore, this makes 3° SN2 substitution not viable. **Steric stress reduction** is the resistance of groups against being forced together. In a 3° carbocation, pushing the groups together for a backside attack increases steric stress. This encourages SN1 substitution **only for 3°** to maintain a tetrahedral geometry. The **positive inductive effect** is the effect that causes more highly substituted carbons to be more stable. Electrons on neighbouring carbon atoms can move closer to the carbon ion, creating an electron-donating effect that slightly balances its charge, increasing its stability and thus window of opportunity for a **SN1** substitution. ### Alcohols An **alcohol** is an organic compound with a $\ce{-OH}$ (hydroxyl) functional group. It has a **higher priority** than double and triple bonds, and alcohol names are suffixed with **-ol**. !!! warning The -ol suffix is a standard suffix following the same numbering rules as -en and -yne. As functional groups are ordered from lowest to highest priority in their name, similar to how a -yne can have an -en, an -ol can also have an -en and **-yn** before it. - Therefore, $\ce{CH3OH}$ is methanol, *not* methol. !!! example Some alcohols and their common names: - **Glycerol**: propan-1,2,3-triol - **Ethyl alcohol** or drinking alcohol: ethanol - **Isopropanol** or rubbing alcohol: propan-2-ol The **type** of an alcohol (primary/secondary/tertiary) is that of the would-be carbocation it is attached to. #### Alcohol combustion Alcohols are combustible, and can undergo complete and incomplete combustion. $$ \ce{alcohol + O2 -> CO2 + H2O (complete) \\ alcohol + O2 -> CO2 + H2O + CO + C (incomplete)} $$ #### Alcohol elimination Under significantly more acidic conditions than hydration, the opposite process can be used to revert an alcohol into its base components. $$\ce{alcohol ->[12 mol/L H2SO4] H2O + alkene}$$ !!! warning When choosing a new double bond to form in the alkene, it must bond to the carbon the OH group was attached to. In elimination, **Markovnikov's rule does not apply**. ### Aldehydes !!! definition - A **carbonyl** is $\ce{C=O}$. - A **hydroxyl** is $\ce{-OH}$. In a side group, it is named **hydroxy**. In the presence of an oxidising agent that is **limited** and acid, **primary** alcohols will oxidise to form aldehydes, where a hydroxyl group becomes a carbonyl group and the hydrogen migrates to the carbon. - $\ce{K2Cr2O7}$ - $\ce{Cr2O7^2-}$ - $\ce{KMnO4}$ - $\ce{MnO4-}$ An aldehyde is named like an alcohol but has a higher naming priority, with a suffix of **-al**. As aldehydes must be at the end of a chain, numbering their position is not required. !!! example - butanal ($\ce{CH3CH2CH2COH}$) - The common name of **methanal** is **formaldehyde**. (Source: Kognity) Aldehydes will continue to react to carboxylic acids if the oxidising agent is not limited. To prevent this, the aldehyde is separated and removed from the mixture through distillation. (Source: Kognity) The mixture is heated to a temperature greater than the aldehyde's boiling point but less than the alcohol's, such that the gaseous aldehyde enters the condenser and is cooled by the water jacket. An aldehyde can also be reduced in a process similar to **hydrogenation** to reverse the reaction. $$\ce{aldehyde + H2 ->[\text{high temp, high pressure, Pt/Pd/Ni}] alcohol}$$ ### Ketones In the presence of an oxidising agent and acid, **secondary** alcohols will oxidise to form ketones, where the hydrogen plops off completely. (Source: Kognity) Because there is no possible reaction afterward (no more hydrogens), distillation is not required. Ketones have equal priority to aldehydes and are named the same but with a suffix of **-one**. A position number *is* required because ketones can be located anywhere on the chain. !!! example - 3-ethyl-4,4-difluoro-5-hydroxylhexan-2-one - 1,1-dibromo-4-cyclopropylhex-5-en-2-one ### Carboxylic acids Aldehydes will react again if there is excess oxidising agent to form a carboxylic acid. (Source: Kognity) Instead of distillation, **reflux** is used to keep the aldehyde in the mixture. The vaporised aldehyde condenses and returns to the mixture. (Source: Kognity) Carboxylic acids have higher priority than aldehydes/ketones and are named the same but with a suffix of **-oic acid**. Similar to aldehydes, because the $\ce{COOH}$ can only exist on the end of a chain, position numbers are omitted. !!! example - **Benzoic acid**: $\ce{benzene-COOH}$ - 3,3-difluoropent-4-enoic acid - 3-ethylhexanedioic acid - The common name of **ethanoic acid** is **acetic acid**. - The common name of **ethanedioic acid** is **oxalic acid**. - The common name of **methanoic acid** is **formic acid**. - Look up citric acid because I'm not writing that down. #### Carboxylic acid salts If the ionising hydrogen is removed ($\ce{COOH -> COO-}$), a carboxylic acid can form a salt by reacting with a metal to form an **ionic compound**. Salts are named as an ionic compound would be, with the acid component resuffixed to **-oate**. $$\ce{R-COOH + NaOH -> R-COONa + H2O}$$ !!! example - sodium ethanoate - lithium benzoate #### Identifying alcohols The **Lucas test** is used to in part determine the type of alcohol (primary/secondary/tertiary) through the **nucleophilic substitution** of OH with Cl. To perform this substitution, **anhydrous** zinc chloride and **concentrated** HCl must be present. $$\ce{R-OH + HCl ->[ZnCl2] R-Cl + H2O}$$ This test is only valid on **small** alcohols because (<6 carbons) as longer ones are insoluble. The insoluble halogenoalkane becomes visible, making the solution **cloudy**. Because the reaction is an SN1 reaction: - Primary alcohols will **not** react - Secondary alcohols react slowly - Tertiary alcohols react rapidly Alternatively, **oxidising** alcohols to aldehydes/ketones through SN2 by reducing $\ce{Cr2O7^2-}$ (orange) to $\ce{Cr^3+}$ (green) will identify the alcohol. - Primary alcohols will react quickly - Secondary alcohols will react slowly - Tertiary alcohols will **not** react ### Ethers !!! definition - A **condensation reaction** or **dehydration synthesis** involves two small molecules reacting to form water and another molecule. Ethers are formed by reacting two alcohols through dehydration synthesis in sulfuric acid. $$\ce{R-OH + HO-R ->[H2SO4] R-O-R + H2O}$$ To name ethers, the shorter alkyl group is named as a side chain while the longer is as the main chain, separated by "oxy". $$\ce{short + oxy + long}$$ Usually, if the "side chain" is at position 1, the position number is omitted. !!! example - pentoxypentane (pentan-1-ol + pentan-1-ol) - 2-ethoxybutane (ethan-2-ol + butan-1-ol) - 2-chloro-3-methoxypentane (chloro is at position 2, methoxy is at position 3 on the pentane) - The common name of **ethoxyethane** is **diethyl ether**. ### Esters When an alcohol and carboxylic acid react in sulfuric acid **and heat**, the only the $\ce{O}$ from the alcohol remains in the ester while that in the acid forms a water. The formed $\ce{COO}$ is known as the **ester linkage**. (Source: Kognity) Esters are named with the alcohol as the side group and the acid as its salt variant with a space in between. If the side chain looks like an alkane, its position number and -ane suffix can be dropped. $$\text{alcohol-yl acid-oate}$$ !!! warning The carbon in the ester linkage is included as a carbon of the main chain of the ester. !!! example - Propyl pentanoate or propan-1-yl pentanoate is formed from propan-1-ol and pentanoic acid. - Propyl 2-chloroethanoate - Hexan-3-yl propanoate Esters hydrolyse to their original components if catalysed by an acid or base. $$\ce{ester + H2O ->[H2SO4] alcohol + carboxylic acid}$$ $$\ce{ester + H2O ->[NaOH] alcohol + RCOONa ->[react with acid] alcohol + carboxylic acid}$$ ### Amines Amines are $\ce{NR3}$ derived from ammonia ($\ce{NH3}$), where R is either H or a carbon group. Similar to alcohols, they can be primary/secondary/tertiary depending on the number of carbon groups attached. The **main chain** is the longest carbon chain. Amines have a priority between double/triple bonds and alcohols, and are named like alcohols but with a suffix of **-amine**. If there are any side groups attached to the nitrogen, they are named as if they were side groups on the main chain with a **number of $N$**. !!! example (Source: Kognity) #### Amine synthesis Amines can be formed through **halogenoalkane substitution**, where ammonia or another amine is alkylated in an SN2 reaction. $$\ce{NH3 + CH3Cl -> CH3NH4Cl ->[OH-] CH3NH2}$$ !!! example $\ce{CH3NH2 + CH3Cl -> CH3NH2CH3Cl ->[OH-] CH3NH2CH3}$ ### Amides Amides are formed from a reaction between an amine and a carboxylic acid through dehydration synthesis, similar to the formation of an ester. The $\ce{N-C=O}$ link is known as the **amide link**. $$\ce{R-COOH + N-R -> R-CON-R}$$ Amides carry the suffix **-amide** and are otherwise named equivalently to esters, but *without* spaces. !!! example (Source: Kognity) ### Nitriles Nitriles consist of a cyanide(s) attached at the end of a carbon chain. $$\ce{R-C#N}$$ As they can only be placed at the end of a carbon chain, a positional number is not used. These have the highest priority of all organic compounds and use the suffix **-nitrile** and the prefix **cyano-**. !!! example - methanenitrile - methanedinitrile Nitriles are synthesised through the nucleophilic substitution of halogenoalkanes, **extending their carbon chain**. $$\ce{R-X + C#N- -> R-C#N + X-}$$ ### Reduction reactions **Hydride reagents** include $\ce{LiAlH4}$ and $\ce{NaBH4}$, the former of which requires ether because it reacts violently with water. Always use $\ce{LiAlH4}$ unless specified otherwise. **Aldehydes** can be reduced to **primary alcohols**. $$\ce{aldehyde ->[LiAlH4, ether, then acid] 1^\circ alcohol}$$ **Amides** can be reduced to their **amines**, reacting twice such that the O pops off. The name is a simple `amide.replace("amide", "amine")`. $$\ce{amide ->[LiAlH4, ether, then acid] amine}$$ !!! warning $\ce{LiAlH4}$ is required for this reaction. **Carboxylic acids** can be reduced to **primary alcohols** with the $\ce{C=O}$ plopping off. $$\ce{carboxylic acid ->[LiAlH4, ether, then acid] 1^\circ alcohol}$$ **Esters** can be reduced to **two primary alcohols** with each alcohol keeping an O and gaining an H to make OH. $$\ce{ester ->[LiAlH4, ether, then acid] 1^\circ alcohol + 1^\circ alcohol}$$ **Nitriles** can be double reduced to **amines**. $$\ce{nitrile ->[LiAlH4, ether, then acid] amine}$$ ### Retro-synthesis Retro-synthesis is basically a language of math but for chem, with products on the left and reactants on the right. The bottom right contains initial reactant(s) and the top left contains the product(s). "A is made from B which is made from C": $$\ce{ A => B react with alcohol using H2SO4 in reflux \\ B => C }$$ !!! example $$\ce{ ethanoic acid => ethanol (react w/K2Cr2O7 in H+) \\ ethanol => chloroethane (react w/warm dilute hydroxide) }$$ ### Simple polymers !!! definition - **Polymers** are large molecules made from many monomers in long chains. - **Plastics** are polymers formed through addition. - A **homopolymer** has identical monomers. - A **heteropolymer** has multiple distinct monomers. - A **monomer** is the repeating segment in a polymer. Polymer properties change based on the type of linkages, the presence of side chains, and the extent of crosslinking between other chains. The **addition formation** of an **addition polymer** opens up pi bonds which are used to bond to other monomers. Monomers are continuously added until the process ends with hydrogen atoms capping the ends. (Source: Kognity) Only the two carbons directly involved in the double bond go in the main chain of the polymer, with all others expressed as side groups. (Source: Kognity) **Polymer notation** is the formula/condensed formula/structural diagram of the **repeating unit only** with crossed out brackets and the number of repetitions at the bottom right (or $n$ if unknown). Side groups should be clearly expressed as side groups. Polymers are named with the prefix **poly-** on the repeating unit. !!! example $$\ce{-(-CH2-CH2-) -_3}$$ #### Crosslinking !!! definition - **Crosslinking** is the bond between side chains of separate polymers, connecting them. The crosslinking between polymers depends on the side chains. If there are multiple double bonds in monomers, those can be used in different chains which can attach them together. !!! example divinylbenzene !!! example If an OH side group meets another OH side group, they may react to form $\ce{O=O}$ and connect the two polymers. ### Polyesters and polyamides !!! definition - **Condensation polymers** are polymers formed via dehydration synthesis and produce water. A **polyester** has monomers connected via an ester linkage on both ends. **Unlike addition polymers**, any carbons between the functional groups are included in the parent polymer chain. (Source: Kognity) The repeating unit should be **copy-pastable** — it should not end with oxygen on both ends. The link is broken where it would normally break — between the C-O of the ester linkage, such that the O goes to the side of the alcohol. (Source: Kognity) A **polyamide** has monomers connected via an amide linkage on both ends. (Source: Kognity) !!! warning There should be a hydrogen attached to the nitrogen at the end of the amine. ### E/Z isomers E/Z isomers are a generalised form of cis-trans isomers, where priority is determined by atomic number. If both sides with the higher atomic number are on the **same** side, the isomer is a Z-isomer (German: *ze zame zide*). E/Z isomers are placed at the beginning surrounded by parentheses. !!! example (Z)-2-bromo-1-chloro-1-fluoroethene: (Source: Kognity) If the atoms are of equal priority, the sum of atomic numbers that they are directly connected to are compared (double bonds count twice), repeating as necessary. !!! example (Z)-1-chloro-1-fluoro-2-methyl-1-butene (left) and (E)-1-chloro-1-fluoro-2-methyl-1-butene (right). (Source: Kognity) If there are multiple E/Z isomers, they are separated by commas and numbered according to their earliest position on the main chain. !!! example (2Z, 3E)-R ### Optical isomers !!! definition - An **enantiomer** is an optical isomer. - A **chiral centre** is a carbon atom with four different groups attached to it. - The **chirality** of a carbon atom represents its ability to form an enantiomer. - A **racemic mixture** is a mixture of exactly one half of each enantiomer of a species such that it is not optically active. - A **dextrorotary** enantiomer rotates rightward (+). - A **levrorotary** enantiomer rotates leftward (-). Optical isomers are mirrored across the y-axis with the same compounds put on the same bonds. **Four distinct groups** must be attached to the central carbon atom to have optical isomers. In the data booklet, all amino acids are chiral except for glycine and proline. !!! example (Source: Kognity) An **optically active** species is one that can rotate the plane of polarised light. Please see [SL Physics 1#Polarisation](/sph3u7/#polarisation) for more information. A species that rotates the plane clockwise is positive, while counter-clockwise is negative. Both enantiomers have the same magnitude of polarisation except for the direction. If there is a mixture of both enantiomers, the angle changes depending on the proportion of each isomer. Enantiomers have the same physical properties except for the direction of polarised light. They also have mostly the same chemical properties except for chemical reactions with other enantiomers of different compounds. ### Properties of organic compounds **Alcohols** are able to form hydrogen bonds, so are soluble in water. Increasing the length of the main chain decreases solubility as the rest of the molecule is non-polar, but this can be compensated by adding more hydroxyls too. In general: - m/ethanols are miscible - butanols are 10-15% v/v miscible - alcohols longer than octanols are effectively insoluble Although the boiling point of an alcohol will always be higher than its corresponding alkane, the difference between the two will decrease as chain length increases as the proportion of force the alcohol provides decreases relative to the larger contributor in the LDF from the main chain. Low mass **esters** smell good, and large mass esters are oily/waxy. **Amines** smell bad and are all Bronsted-Lowry weak bases because they can accept protons and form dative bonds. The solubility of compounds is directly related to their melting/boiling point — compounds that cannot hydrogen bond with themselves but can with water have an advantage. From greatest to lowest melting point: **Hydrogen bonding** - Water is able to hydrogen bond with two other molecules per molecule, efficiently using all its lone pairs and Hs. - Carboxylic acids are less efficient than water but more than alcohols as an the OH can attract to an O on a different molecule. - Alcohols - Primary/secondary amines can hydrogen bond but the N-H bond is less polar than O-H, decreasing its strength. **Dipole-dipole interaction** - Aldehydes and ketones - Esters are less polar than aldehydes because the single bond O attracts electrons from the C=O. - Ethers have horizontal components to their dipole vectors that cancel out, so they are least polar. **London dispersion forces** - Alkynes' triple bonds means that packing is easier, increasing LDFs. - Alkanes - Alkenes' double bonds means that there are less electrons than their alkane counter parts, reducing LDFs. $$\ce{ water >> \\ carboxylic acids > alcohols > amines >> \\ ethers > aldehydes/ketones >> \\ alkynes > alkanes > alkenes }$$ ## Resources - [IB Chemistry Data Booklet](/resources/g11/ib-chemistry-data-booklet.pdf) - [IB HL Chemistry Syllabus](/resources/g11/ib-chemistry-syllabus.pdf) - [Significant Figures/Digits](/resources/g11/chemistry-sig-figs.pdf) - [Error Analysis and Significant Figures (long)](/resources/g11/error-analysis-sig-figs.pdf) - [General Guidelines for Writing a Formal Laboratory Report](/resources/g11/lab-report-guidelines.pdf) - [Designing an IB Investigation](/resources/g11/designing-investigation.pdf) - [Textbook: Pearson Higher Level Chemistry](/resources/g12/textbook-hl-chem.pdf) ([Answers](/resources/g12/textbook-hl-chem-answers.pdf)) - [mini Eifueo](/resources/g12/textbook-hl-chem-eifueo.pdf)