134 REACTIONS OF ALKENES: ADDITION REACTIONS (c) HBr H3 1-lodo-1-methylcyclohexane CH hO I-Methylcyclohexanol (f) H 2. H,O2.HO trans-2-Methylcyclohexano CH h) CH CH trans-2-Bromo.I methylcyclohexane CH CH-COOH DO +CH,CO,H 1, 2-Epoxy-l-methylcyclohexane (j) H3 C H3 O CH, CCH, CH, CH, CH, CH 6-Oxoheptanal Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(c) (d) (e) ( f ) (g) (h) (i) ( j) (k) HO O CH3 O O O CH3 H2O Zn CH3CCH2CH2CH2CH2CH O O 6-Oxoheptanal O O O CH3 CH3 O3 Ozonide O CH CH3 3 CH3CO2OH CH3CO2H 1,2-Epoxy-1-methylcyclohexane CH3 Br 2 trans-2-Bromo-1- methylcyclohexanol H2O OH CH3 Br CH3 Br 2 trans-1,2-Dibromo-1- methylcyclohexane Br CH3 Br CCl4 CH3 trans-2-Methylcyclohexanol CH3 H OH 1. B2H6 2. H2O2, HO CH3 H2O 1-Methylcyclohexanol CH3 H2SO4 OH CH3 HI 1-Iodo-1-methylcyclohexane CH3 I CH3 HBr CH3 Br 1-Bromo-2-methylcyclohexane (mixture of cis and trans) peroxides 134 REACTIONS OF ALKENES: ADDITION REACTIONS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
REACTIONS OF ALKENES: ADDITION REACTIONS 135 6.25 We need first to write out the structures in more detail to evaluate ubstitution patterns at the double bonds (a) 1-Pentene Monosubstituted (b)(E)-4, 4-Dimethyl-2-pentene trans-Disubstituted (c)(2)-4-Methyl-2-pentene cis-Disubstituted (d)(2)-2, 2,5. 5-Tetramethyl-3-hexene Two tert-butyl grot (e) 2, 4-Dimethyl-2-pentene Trisubstituted Compound d, having two cis tert-butyl groups, should have the least stable(highest energy)double bond. The remaining alkenes are arranged in order of increasing stability(decreasing heats of hydrogenation)according to the degree of substitution of the double bond: monosubstituted, cis disubstituted, trans-disubstituted, trisubstituted. The heats of hydrogenation are therefore 51 kJ/ mol (36.2 kcal/mol) 122 kJ/mol (29.3 kcal/mol) 114 kJ/mol(27.3 kcal/mol (b) 11 kJ/mol(26.5 kcal/mol) 105 kJ/mol(25.1 kcal/mol 6.26 In all parts of this exercise we deduce the carbon skeleton on the basis of the alkane formed on hydrogenation of an alkene and then determine what carbon atoms may be connected by a double bond in that skeleton. Problems of this type are best done by using carbon skeleton formul (a) Product is 2, 2, 3, 4, 4-pentamethylpentane. The only possible alkene precursor is (b) Product is 2, 3-dimethylbutane May be formed by hydrogenation of (c) Product is methylcyclobutane May be formed by hydrogenation of Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
6.25 We need first to write out the structures in more detail to evaluate the substitution patterns at the double bonds. (a) 1-Pentene Monosubstituted (b) (E)-4,4-Dimethyl-2-pentene trans-Disubstituted (c) (Z)-4-Methyl-2-pentene cis-Disubstituted (d) (Z)-2,2,5,5-Tetramethyl-3-hexene Two tert-butyl groups cis (e) 2,4-Dimethyl-2-pentene Trisubstituted Compound d, having two cis tert-butyl groups, should have the least stable (highest energy) double bond. The remaining alkenes are arranged in order of increasing stability (decreasing heats of hydrogenation) according to the degree of substitution of the double bond: monosubstituted, cisdisubstituted, trans-disubstituted, trisubstituted. The heats of hydrogenation are therefore: (d) 151 kJ/mol (36.2 kcal/mol) (a) 122 kJ/mol (29.3 kcal/mol) (c) 114 kJ/mol (27.3 kcal/mol) (b) 111 kJ/mol (26.5 kcal/mol) (e) 105 kJ/mol (25.1 kcal/mol) 6.26 In all parts of this exercise we deduce the carbon skeleton on the basis of the alkane formed on hydrogenation of an alkene and then determine what carbon atoms may be connected by a double bond in that skeleton. Problems of this type are best done by using carbon skeleton formulas. (a) The only possible alkene precursor is Product is 2,2,3,4,4-pentamethylpentane. (b) May be formed by hydrogenation of Product is 2,3-dimethylbutane. or (c) May be formed by hydrogenation of Product is methylcyclobutane. or or REACTIONS OF ALKENES: ADDITION REACTIONS 135 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website