Page Minto - Lectures Chapter 4 - “Alcohols and Alkyl Halides” 1)Functional groups and nomenclature 2)Role of intermolecular forces on properties 3)Synthesis of alkyl halides from alcohols 4)Two reaction mechanisms: S N 1 and S N 2 cation stability and the Hammond Postulate 5)Additional ways to prepare RX from ROH 6)Halogenation of alkanes: reactivity- selectivity principle, radical stability and chain reactions All sections are covered.

Page Minto - Lectures Functional Groups and Priorities Nomenclature assembles names like trees: start with a parent structure (e.g., an alkane), then add prefixes and a functional group (FG) suffix. FGs are the centers of reactivity within molecules and have predictable chemical behavior. In naming, FGs are usually higher priority than a substituent. In more complicated names, FGs can be indicated by a prefix. IUPAC naming of acyclic compounds Double and triple bonds are incorporated into the parent chain, as much as possible, resulting in a modified hydrocarbon name. Beyond their presence in the parent chain, they are numbered in a prioritized fashion with any other FGs that are present.

Page Minto - Lectures FG Priority List High Carboxylate Carboxylic acid Anhydride Ester Acid halide Amide Nitrile Aldehyde Ketone Alcohol (phenol) Amine Ether Alkene Alkyne Alkyl halide, phenyl, alkyl Low

Page Minto - Lectures IUPAC Nomenclature of Alkyl Halides 1. In the formal IUPAC system, alkyl halides are named as substituted alkanes: F, fluoro; Cl, chloro; Br, bromo; I, iodo. In common naming, they are named as halides (e.g., methyl chloride). 2. Halogens are treated as substituents of equal priority to alkyl groups. 4-chloro-3,3-dimethyl-6-(1-methylethyl)nonane or 4-chloro-6-isopropyl-3,3-dimethylnonane 4-bromo-2-iodo-1-methylcyclohexane

Page Minto - Lectures Classification of Alkyl Halides n-butyl bromide (common) or 1-bromobutane (IUPAC) sec-butyl bromide (common) or 2-bromobutane (IUPAC) tert-butyl bromide (common) Or 2-bromo-2-methylpropane (IUPAC) 1°2° 3°

Page Minto - Lectures Nomenclature of Alcohols In an alcohol, the OH is a high-priority functional group. IUPAC NAME = substituent prefixes+parent+functional group suffix(es). For alcohols, alkane suffix “e” changes to “ol”. 1. Determine the parent hydrocarbon containing the functional group. On cyclic compounds, OH receives number “1”; only show the “1” if multiple OH groups are present. 2. If necessary, the suffix is preceded by a positional identifier. ** **both o.k. as formal names **

Page Minto - Lectures ° 2° 3° Alcohols can be categorized as primary (1°), secondary (2°), and tertiary (3°) by the number of carbons directly attached to the hydroxyl-bearing carbon.

Page Minto - Lectures butanamine or butan-1-amine A primary (1°) amine, one C attached to N Classification of amines is different than ROH or RX. N-ethyl-3-heptanamine A secondary (2°) amine, two C attached to N 2-ethyl-N-methyl-N-propylcyclohexanamine A tertiary (3°) amine, three C attached to N

Page Minto - Lectures Hybridization and Bonding in ROH  = 1.7 D  = 1.9 D MeOHMeCl

Page Minto - Lectures Recall: A hydrogen bond is a very strong dipole–dipole interaction: ONLY occurs when N-H, O-H, and F-H bonds (H-bond donors) interact with N, O, and F atoms (H-bond acceptors). Solubility of hydrogen-bondable molecules in water depends upon their proportion of H-bond donor/acceptor atoms.

Page Minto - Lectures CH 3 CH 2 CH 3 CH 3 CH 2 F CH 3 CH 2 OH Molecular weight Boiling point, °C Dipole moment, D Effect of Structure on Boiling Point

Page Minto - Lectures Polarizability Distortion of electron clouds is important to van der Waals attractive interactions (induced dipole-induced dipole). Increasing the atomic radii within a group raises the boiling point.

Page Minto - Lectures Example: Boiling point increases with increasing number of halogens CH 3 Cl -24°C CH 2 Cl 2 40°C CHCl 3 61°C CCl 4 77°C CompoundBoiling Point Even though CCl 4 is the only compound in this list without a dipole moment, it has the highest boiling point. Induced dipole-induced dipole forces are greatest in CCl 4 because it has the greatest number of Cl atoms. Cl is more polarizable than H. Zero dipole moment

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Page Minto - Lectures Reaction Mechanisms We will dissect the reactions of alcohols with HX to make alkyl halides to learn about reaction mechanisms. There are two main reaction types S N 1 and S N 2. We will define these names in a few minutes. Example: (CH 3 ) 3 COH + HCl > (CH 3 ) 3 CCl + HOH This reaction is a substitution reaction, but the net reaction does not give the details of the reaction mechanism, or path. Ten new terms: Elementary stepIntermediate Transition stateOxonium ion Activation barrierCarbocation Concerted reactionNucleophile MolecularityElectrophile

Page Minto - Lectures Reaction Pathway Energy Barrier Intermediate 2 nd intermediate Products

Page Minto - Lectures tert-butanol + HCl, 1 st elementary step pK a -3.9 pK a -2 Intermediates

Page Minto - Lectures tert-butanol + HCl, 2 nd elementary step Hammond Postulate: If the structure of a transition state is similar in energy to the species immediately preceding or following it, the transition state structure will most resemble that species.

Page Minto - Lectures tert-butanol + HCl, 3 rd elementary step Alkyl Chloride

Page Minto - Lectures Potential Energy Diagram of S N 1 Reaction of an Alcohol with HX Rate = k[alkyloxonium ion] Mechanisms can be supported or disproved, but cannot be proven correct.