6.2 Heats of Hydrogenation TABLE 6.1 Heats of Hydrogenation of Some Alkenes Heat of hydrogenation Alkene Structure k/mol kcal/mol Ethylene Monosubstituted alkenes Propene H=CHCH 299 1-Butene CH2-CHCH2 CH 1-Hexene CH2-CHCH? CH2 CH2 CH3 30.2 Cis-disubstituted alkenes H3C Cis-2-Butene 119 Cis-2-Pentene Trans-disubstituted alkenes H3C trans-2-Butene 27.4 CH rans-2-Pentene C=C 27.2 CH2 CH3 Trisubstituted alkenes 2-Methyl-2-pentene (CH3)2C-CHCH2 CH3 26.7 Tetrasubstituted alkenes 2, 3-Dimethyl-2-butene (CH3)2C-C(CH3)2 exact the pattern of alkene stability determined from heats of hydrogenation parallels tly the pattern deduced from heats of combustion. Decreasing heat of hydrogenation and increasing stability of the double bond CH2-CH2 RCHECH RCH=CHR R2C-CHR R2C=CR2 Ethylene Disubstituted Trisubstituted Tetrasubstituted Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteThe pattern of alkene stability determined from heats of hydrogenation parallels exactly the pattern deduced from heats of combustion. Decreasing heat of hydrogenation and increasing stability of the double bond R2C CR2 Tetrasubstituted R2C CHR Trisubstituted RCH CHR Disubstituted RCH CH2 Monosubstituted CH2 CH2 Ethylene 6.2 Heats of Hydrogenation 211 TABLE 6.1 Heats of Hydrogenation of Some Alkenes Heat of hydrogenation kcal/mol 29.9 30.1 30.2 28.4 32.6 27.4 27.2 26.7 26.4 28.1 kJ/mol 125 126 126 119 117 136 115 114 112 110 Alkene Propene 1-Butene 1-Hexene cis-2-Butene Monosubstituted alkenes Cis-disubstituted alkenes trans-2-Butene trans-2-Pentene Trans-disubstituted alkenes 2-Methyl-2-pentene Trisubstituted alkenes cis-2-Pentene 2,3-Dimethyl-2-butene Tetrasubstituted alkenes Ethylene Structure CH2 CH2 CH2 CHCH3 (CH3)2C CHCH2CH3 (CH3)2C C(CH3)2 CH2 CHCH2CH3 CH2 CHCH2CH2CH2CH3 H3C C CH3 H H C H3C C CH2CH3 H H C H3C C H H CH3 C H3C C H H CH2CH3 C Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website