1559T.ch03.38-5410/22/052:59Page44 EQA 44.Chapter 3 REACTIONS OF ALKANES Two possible hydrogen abstractions can occur: H aa+an一+atcw 气H Abstraction only occurs from the carbon next to a radical carbon.Methyl radical.CH.doesn't have another carbon next to its radical center.so it cannot give up a hydrogen in an abstraction.It can still acking of propane:methane,ethane.butane,and ethen 16.(a)The weakest bond in butane is the C2-C3 bond.DH=88 kcal mol-!(Table 3-2).Pyrolysis should therefore proceed as follows: ①CH,c闻间6H,CH,一2CH,C:c-Cbd deag (2)2CH,CH2·一CHCH2CH,CH Reverse of(1) Ethane (b)The weakest bonds are the three equivalent C-Cbonds.D=88 kcal molTherefore. @2a一 (6)2(CH2CH ④CH,CHCH一(CH,CH Revene of ()bi 句cH,fYam6ch一GL+cH=ca,lyop nc (6)(CHCH.HCHCHCH,-CH,CH.CH +CH:-CHCH, Propane Propene 17.The D data are readily found (Tables 3-1 and 3-4).Values in kcal mol- (a)104+38-2136)=-130 (b)104+58-2103)=-44 (c)104+46-2(87)=-24 (d104+36-2(71)=-2 (e)96.5+38-(110+136)=-1115 f)96.5+58-(85+103)=-335 (g)96.5+46-(71+87)=-15.5 h)96.5+36-(55+71)=+6.5Two possible hydrogen abstractions can occur: (e) (f ) Abstraction only occurs from the carbon next to a radical carbon. Methyl radical, jCH3, doesn’t have another carbon next to its radical center, so it cannot give up a hydrogen in an abstraction. It can still accept a hydrogen, however [reaction (e), above]. So there are four new products formed from cracking of propane: methane, ethane, butane, and ethene (ethylene). 16. (a) The weakest bond in butane is the C2OC3 bond, DH° 88 kcal mol1 (Table 3-2). Pyrolysis should therefore proceed as follows: (1) (2) (3) (b) The weakest bonds are the three equivalent COC bonds, DH° 88 kcal mol1 . Therefore, (1) (2) (3) (4) (5) (6) 17. The DH° data are readily found (Tables 3-1 and 3-4). Values in kcal mol1 . (a) 104
38  2(136) 130 (b) 104
58  2(103) 44 (c) 104
46  2(87) 24 (d) 104
36  2(71) 2 (e) 96.5
38  (110
136) 111.5 (f ) 96.5
58  (85
103) 33.5 (g) 96.5
46  (71
87) 15.5 (h) 96.5
36  (55
71)
6.5 (CH3)2CH Propane Propene H CH2 CHCH3 CH3CH2CH3
CH2 CHCH3 CH3 Hydrogen abstractions Methane Propene H CH2 CHCH3 CH4
CH2 CHCH3 CH3 CH(CH3)2 (CH3)3CH Reverse of (1); recombinations 2,3-Dimethylbutane 2 (CH3)2CH (CH3)2CHCH(CH3)2 Ethane 2 CH3 CH3CH3 (CH3)2CH (CH CH3 3)2CH CH
3 Cleavage Hydrogen abstraction Ethane Ethene CH3CH2 H CH CH2 CH2 3CH3
CH2 CH2 2 CH3CH2 CH3CH2CH2CH3 Reverse of (1) CH3CH2 CH2CH3 2 CH3CH2 C—C bond cleavage Ethane Ethene CH3CH2
CH3CH3
CH2 CH2 H CH2 CH2 Methane Ethene CH3
CH4
CH2 CH2 H CH2 CH2 44 • Chapter 3 REACTIONS OF ALKANES 1559T_ch03_38-54 10/22/05 2:59 Page 44