1559p.eh0338-5410/22/052:59Pmge46 EQA 46.Chapter 3 REACTIONS OF ALKANES Yield of 2-chloro-3-methylpentane=100%x 16/30=53% oromethyl)pentane 00% (c)Propagation step 1 [values below are D(kcal mol)for bonds made or broken] CH3 CH.CH CHCH CH+Cl.HCI+CHCH.CCH.CH 1034=96.5-103=-6 Propagation step 2: CHs CHCH2CCH-CH;+Cl-Cl.+CH;CH2CCICH2CH3 58 85△r=-27 For the reaction overall.A=-33.5 kcal mol Br2-2Br Propagation: ()Br·+CHL一CH·+HBr (2②CH+Br2一CBr+Br Termination: Br.+Br 一B2 CH3·+Br·→CHB →CHCH 21.Initiation: Br2一2Br H=+46 kcal mol- Propagation: Br·+C6H6一HBr+Casr=+25 keal mol- (②)CH+B2- →C.HsBr+Br· 4°=-35 kcal mol- Overall △=-l0 kcal mol determining first propagation step in the reaction of benzene is much more endothermic than any of theSo, Yield of 1-chloro-3-methylpentane 100%  6/(6
16
5
3) 100%  6/30 20% Yield of 2-chloro-3-methylpentane 100%  16/30 53% Yield of 3-chloro-3-methylpentane 100%  5/30 17% Yield of 3-(chloromethyl)pentane 100%  3/30 10% (c) Propagation step 1 [values below are DH° (kcal mol1 ) for bonds made or broken]: Propagation step 2: For the reaction overall, H° 33.5 kcal mol1 . 20. The mechanism is qualitatively the same as that of chlorination of methane (textbook Section 3-4): Initiation: Propagation: (1) (2) Termination: 21. Initiation: Propagation: (1) (2) The overall H° is not very different from those of typical alkane COH bonds: methane, H° 6 kcal mol1 ; 1° COH, H° 10; 2° COH, H° 13.5; 3° COH, H° 15.5. However, the rate￾determining first propagation step in the reaction of benzene is much more endothermic than any of the C6H5 Br2 C6H5Br Br Overall

H 35 kcal mol1 H 10 kcal mol1 Br
C6H6 HBr
C6H5 H
25 kcal mol1 Br2 2 Br H
46 kcal mol1 Br
Br Br2 CH3
Br CH3Br CH3
CH3 CH3CH3 CH3
Br2 CH3Br Br
Br
CH4 CH3
HBr Br2 2 Br 58 85 H 27 CH3 CH3CH2CCH2CH3
Cl2 Cl CH3
CH3CH2CClCH2CH3 96.5 103 H 96.5  103 6.5 CH3CH2CHCH2CH3 CH3 CH3
Cl HCl CH
3CH2CCH2CH3 46 • Chapter 3 REACTIONS OF ALKANES 1559T_ch03_38-54 10/22/05 2:59 Page 46