CONJUGATION IN ALKADIENES AND ALLYLIC SYSTEMS 233 (c) The C-1 and C-3 bonds of cembrene are conjugated with each other. CH (CH3)2CH CH The double bonds at C-6 and C-10 are isolated from each other and from the conjugated diene (d) The sex attractant of the dried-bean beetle has a cumulated diene system involving C-4, C-5, and C-6. This allenic system is conjugated with the C-2 double bond CH3(CH2)CH, CH=C=CHCH=CHCO, CH 10.7 The more stable the isomer, the lower its heat of combustion. The conjugated diene is the most stable and has the lowest heat of combustion the cumulated diene is the least stable and has the highest heat of combustion HC H,C=CHCH, CH=CH, H,C=C=CHCH, CH3 (E)-1, 3-Pentadiene 1. 4-Pentadiene Most stabl 3186 kJ/mol (68.9 kcal/mol) 3251 (761.6 kcal/mol) (777.1 kcal/mol) 10.8 Compare the mirror-image forms of each compound for superposability. For 2-methyl-2, 3- pentadiene 2-methyl-2, 3-pentadiene H-C H,C. CH3 H-C H C unit demonstrates that the reference structure and its mirror image are superposable he Rotation of the mirror image 180 around an axis passing through the three carbons of th H C. CH CH H CH Mirror image 2-Methyl-2, 3-pentadiene is an achiral allene Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website(c) The C-1 and C-3 double bonds of cembrene are conjugated with each other. The double bonds at C-6 and C-10 are isolated from each other and from the conjugated diene system. (d) The sex attractant of the dried-bean beetle has a cumulated diene system involving C-4, C-5, and C-6. This allenic system is conjugated with the C-2 double bond. 10.7 The more stable the isomer, the lower its heat of combustion. The conjugated diene is the most stable and has the lowest heat of combustion. The cumulated diene is the least stable and has the highest heat of combustion. 10.8 Compare the mirror-image forms of each compound for superposability. For 2-methyl-2,3- pentadiene, Rotation of the mirror image 180° around an axis passing through the three carbons of the C?C?C unit demonstrates that the reference structure and its mirror image are superposable. 2-Methyl-2,3-pentadiene is an achiral allene. C Rotate 180 Mirror image C H CH3 H3C CH3 C Reoriented mirror image C C H3C H H3C CH3 C 2-methyl-2,3-pentadiene and Reference structure C C H3C H H3C CH3 C Mirror image C C H CH3 H3C CH3 C H2C CHCH2CH CH2 H2C C CHCH2CH3 (E)-1,3-Pentadiene Most stable 3186 kJ/mol (761.6 kcal/mol) 1,4-Pentadiene 3217 kJ/mol (768.9 kcal/mol) 1,2-Pentadiene Least stable 3251 kJ/mol (777.1 kcal/mol) C C H H3C H CH CH2 CH3(CH2)6CH2CH C CHCH CHCO2CH3 6 54 3 2 1 (CH3)2CH CH3 CH3 CH3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Cembrene CONJUGATION IN ALKADIENES AND ALLYLIC SYSTEMS 233 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website