A. General. Structure, Nomenclature and Physical Properties Haloalkanes Alcohols Amines

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Haloalkanes, Alcohols and Amines, Lecture 1 A. General. Structure, Nomenclature and Physical properties Haloalkanes Alcohols Amines

Structure: R X Structure: Oxygen sp3 hydbridised with Structure: N is sp3 hybridised with lone pair two lone pairs 1.43 Å (c.f. C-C R=Alkyl: 1.47 Å; R=H: 1.04 Å halogen: (F), Cl, Br, I R alkyl 1.54Å) shortening of C-O and O-H O due to increasing electro- R R H R negativity of O (3.44) vs N R N Bond length (Å) Dipole Moment (D) 0.96 Å (c.f. C-H C (2.55) R R 1.10Å) Cl 1.76 1.85 pyramidal: but undergoes rapid inversion: ca 2 x 1011 s-1 Br 1.93 1.8 Alcohols participate in Hydrogen-bonding I 2.13 1.6 ca 400 R -1 R δ− kJmol δ− δ+ δ+ O δ+ O δ+ H δ− H δ− H H O O R R Hydrogen bond 2.07 Å,ca 20 kJmol-1

Nomenclature: Depending on the Nomenclature: As for the alkyl halides we classify Nomenclature: substitutionof the carbon bearing the alkyl alcohols as 1û, 2û or 3û. halogen atom we classify alkyl R NH2 R NH R N R halides as primary (1û), secondary H R R R R (2û) or tertiary (3û). R C OH R C OH R C OH 1û 2û 3û H H R H R R 1û 2û 3û R C X R C X R C X Beware confusion here: e.g., "tert-butylamine", Me CNH is a 1û amine. H H R 3 2 1û 2û 3û Haloalkanes, Alcohols and Amines, Lecture 1

Haloalkanes have higher boiling points Physical Properties: Physical properties: (bp's) than the corresponding alkanes: Hydrogen bonding is weak, but their cumulative effect Amines have a characteristic "fishy" odour. is considerable and responsible for: the anomalously e.g., CH4 CH3Cl CH3Br CH3I Amines have higher bp's than non-polar -162ûC -24ûC 5ûC 43ûC high bp's of alcohols compounds of similar molecular weight e.g. MeL EtL PrL BuL H CNH (MW 31) CH CH NH (MW 45) Boiling points increase ca 20-30ûC in the L = H -162ûC -88ûC -42ûC 0ûC 3 2 3 2 2 homolgous series L = OH 64ûC 78ûC 97ûC 118ûC bp: -7.5ûC bp: 49ûC CH3CH 3 (MW 30) CH3CH 2CH3 (MW 44) e.g., MeI EtI PrI BuI bp: -88ûC bp: -42ûC 43ûC 72ûC 102ûC 130ûC Hydrogen bonding is also responsible for the solubility of low molecular weight alcohols in Neat, 1û and 2û (but not 3û) amines can water: intermolecularly hydrogen-bond: Branching lowers bp's: C6H13 NH2: bp 131ûC Compound: Solubility (g/100g H2O) (C3H7)2NH: bp 110ûC (C2H5)3N: bp 89ûC MeOH ∞ Br Br Br Br EtOH ∞ 130ûC 120ûC 119ûC 100ûC PrOH ∞ 1û, 2û and 3û amines can all Hydrogen-bond dec. BuOH 7.9 to water. Therefore the low MW amines (

Haloalkanes are insoluble in water; Haloalkanes are soluble in common organic solvents;

I, Br and poly-Cl alkanes are more dense than water. B. Reactivity

Haloalkanes Alcohols Amines

Good electrophiles for nucleophilic Alcohols are only relative weak nucleophiles, Lone pair renders amines nucleophilic. Substitution by breaking of C-X bond. but when deprotonated are good nucleophiles and good bases.