ALCOHOLS AND ALKYL HALIDES 69 4.7 Since the pk, of HCN is given as 9.1, its K=10.. In more conventional notation, K 8X10. Hydrogen cyanide is a weak acid 4.8 Hydrogen cyanide is a weak acid, but it is a stronger acid than water(pK= 15.7). Since HCN is a stronger acid than water, its conjugate base(Cn )is a weaker base than hydroxide(Ho), which the conjugate base of water. 4.9 An unshared electron pair on oxygen abstracts the proton from hydrogen chloride CHD),C. co +HC Co-H + :C: B Acid Conjugate 4.10 In any proton-transfer process, the position of equilibrium favors formation of the weaker acid and the weaker base from the stronger acid and base. Alkyloxonium ions(ROH, t) have approximately the same acidity as hydronium ion(H,o, pk=-1.7). Thus hydrogen chloride(pK,"-7)is the stronger acid. tert-Butyl alcohol is the stronger base because it is the conjugate of the weaker acid (tert-butyloxonium ion) (CH3)3COH HCI (CH3)3COH2 CI The equilibrium constant for proton transfer from hydrogen chloride to tert-butyl alcohol is much greater than 1 4.11 The proton being transferred is partially bonded to the oxygen of tert-butyl alcohol and to chloride at the transition state 8-+-c 4.12 (b) Hydrogen chloride converts tertiary alcohols to tertiary alkyl chlorides (CH,CH,)COH (CH,CH2)3CCI H,O 3-Ethyl-3-pentanol 3-Chloro-3-ethylpentane (c) 1-Tetradecanol is a primary alcohol having an unbranched 14-carbon chain. Hydrogen bromide reacts with primary alcohols to give the corresponding primary alkyl bromide CHa(CH2)12CH,OH HBr CHa(CH)) CH,Br H,O Hydrogen 4.13 The order of carbocation stability is tertiary secondary primary. There is only one CsH,car- bocation that is tertiary, and so that is the most stable one. CH3,C+ 1, 1-Dimethylpropyl cation Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website4.7 Since the pKa of HCN is given as 9.1, its Ka  109.1. In more conventional notation, Ka  8  1010. Hydrogen cyanide is a weak acid. 4.8 Hydrogen cyanide is a weak acid, but it is a stronger acid than water (pKa  15.7). Since HCN is a stronger acid than water, its conjugate base (CN) is a weaker base than hydroxide (HO), which is the conjugate base of water. 4.9 An unshared electron pair on oxygen abstracts the proton from hydrogen chloride. 4.10 In any proton-transfer process, the position of equilibrium favors formation of the weaker acid and the weaker base from the stronger acid and base. Alkyloxonium ions (ROH2 ) have approximately the same acidity as hydronium ion (H3O, pKa  1.7). Thus hydrogen chloride (pKa 7) is the stronger acid. tert-Butyl alcohol is the stronger base because it is the conjugate of the weaker acid (tert-butyloxonium ion). The equilibrium constant for proton transfer from hydrogen chloride to tert-butyl alcohol is much greater than 1. 4.11 The proton being transferred is partially bonded to the oxygen of tert-butyl alcohol and to chloride at the transition state. 4.12 (b) Hydrogen chloride converts tertiary alcohols to tertiary alkyl chlorides. (c) 1-Tetradecanol is a primary alcohol having an unbranched 14-carbon chain. Hydrogen bromide reacts with primary alcohols to give the corresponding primary alkyl bromide. 4.13 The order of carbocation stability is tertiary  secondary  primary. There is only one C5H11 car￾bocation that is tertiary, and so that is the most stable one. 1,1-Dimethylpropyl cation CH3CH2C CH3 CH3 CH3(CH2)12CH2OH HBr 1-Tetradecanol CH3(CH2)12CH2Br Hydrogen 1-Bromotetradecane bromide H2O Water (CH3CH2)3COH HCl 3-Ethyl-3-pentanol (CH3CH2)3CCl Hydrogen 3-Chloro-3-ethylpentane chloride H2O Water O H Cl H (CH3)3C (CH3)3COH HCl Cl Stronger base (pKa 7) Stronger acid (CH3)3COH2 (pKa 1.7) Weaker acid Weaker base Acid H Cl H Conjugate base Cl Conjugate acid O (CH3)3C H Base O (CH3)3C H ALCOHOLS AND ALKYL HALIDES 69 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website