b.断链反应 R-CH-Ch-RR-CH=Ch+Rh 或Cm+nH2m++2→CmH2m+CnH2n+2 各种键能比较 碳氢键 键能kJ/mol 键能,kJ/mol H3C-H 426.8 CH3-CH CH3]-H 405.8 CH3-CH2-CH3 343.1 CH: CH, CH,-H 397.5 CH3 CH -, CH3 CH3-CH(CH3)H 384.9 CH3, 3418 CH3 CH2 CH2-H 393.2 H3C-C(CH3) 314.6 CH3 CH2CH(CH3)H 376.6 CH3CH2CH2-CH2CH2CH3325.1 CH3- C(CH3hH 364 CH3CH(CH3)-CH(CH3)CH3 310.9 C-H(一般) 378.7 裂解反应规律 ☆相同碳原子的烷烃,E∽>Ec,故断链较脱氢容易 ☆烷烃的相对热稳定性随碳链的增长而降低,即碳链越长的烃分子愈易裂解 ☆烷烃的脱氢能力与烷烃的分子结构相关,叔、仲、伯氢脱氢能力依次减弱 ☆支链的ECC、ECH均小于直链的Ecc、FCH,故异构烷烃更易断链或脱氢; 正构烷烃一次反应的△G°和△H"(100 反应 Chie echo+h 31.0 脱 ChabC + -8.08 1308 C6H12>C6H2+H2 741 130.8 C4H10→C3H6+CH4 66.5 C4H10→>C2H4+C2H6 -42.34 88.6 C5H12→>C4H8+CH4 -6908 65.4 链 C5H12→C3H6+C2H6 -61.13 C5H2→>C2H4+C3H 90.1 C6H4→C5H1o+CH4 70.08 66.6 C6H4→C4H8+C2H6 75.5b．断链反应 m n 2(m n) 2 m 2m n 2n 2 ' 2 ' 2 2 C H C H C H R - CH - CH - R R - CH CH R H + + + → + + → = + 或 各种键能比较 碳 氢 键 键能,kJ/mol 碳 碳 键 键能，kJ/mol H3C-H 426.8 CH3-CH3 346 CH3CH2-H 405.8 CH3-CH2-CH3 343.1 CH3CH2CH2-H 397.5 CH3CH2-CH2CH3 338.9 CH3-CH(CH3)H 384.9 CH3CH2CH2-CH3 341.8 CH3CH2CH2CH2-H 393.2 H3C-C(CH3)3 314.6 CH3CH2CH(CH3)H 376.6 CH3CH2CH2-CH2CH2CH3 325.1 CH3-C(CH3)2H 364 CH3CH(CH3)-CH(CH3)CH3 310.9 C-H(一般) 378.7 裂解反应规律： ☆相同碳原子的烷烃，EC-H﹥EC-C，故断链较脱氢容易； ☆烷烃的相对热稳定性随碳链的增长而降低，即碳链越长的烃分子愈易裂解； ☆烷烃的脱氢能力与烷烃的分子结构相关，叔、仲、伯氢脱氢能力依次减弱； ☆支链的 EC-C、EC-H均小于直链的 EC-C、EC-H，故异构烷烃更易断链或脱氢； 正构烷烃一次反应的ΔGθ和ΔHθ (1000K) 反应 ΔGθ 1000K kJ／mol ΔHθ 1000K kJ／mol C4H10 ↔ C4H8 + H2 -5.94 131.0 C5H12 ↔ C5H10 + H2 -8.08 130.8 脱 氢 C6H12 ↔ C6H12 + H2 -7.41 130.8 C4H10 → C3H6 + CH4 -68.99 66.5 C4H10 → C2H4 + C2H6 -42.34 88.6 C5H12 → C4H8 + CH4 -69.08 65.4 C5H12 → C3H6 + C2H6 -61.13 75.2 C5H12 → C2H4 + C3H8 -42.72 90.1 C6H14 → C5H10 + CH4 -70.08 66.6 断 链 C6H14 → C4H8 + C2H6 -60.08 75.5