STRUCTURE AND PREPARATION OF ALKENES: ELIMINATION REACTIONS (f Two alkenes may be formed here. The more highly substituted one is 1-methylcyclohexene and this is predicted to be the major product in accordance with Zaitsev's rule H I-lodo-1-methylcyclohexane methylenecyclohexane 1-Methylcyclohexene (disubstituted) 5.18 Elimination in 2-bromobutane can take place between C-1 and C-2 or between C-2 and C-3. Ther are three alkenes capable of being formed: 1-butene and the stereoisomers cis-2-butene and trar 2-butene HC CH3 H3C CH3 CHCH,CH3 CH2=CHCH,CH3+ 2-Bromobutane cis-2-Butene As predicted by Zaitsev's rule, the most stable alkene predominates. The major product is trans 2-butene 5.19 An unshared electron pair of the base methoxide(CHao )abstracts a proton from carbon. The pair of electrons in this C-H bond becomes the T component of the double bond of the alkene. The pair of electrons in the C-Cl bond becomes an unshared electron pair of chloride ion CH,O: H CH CH一H+H2C=CCH3)2+Q! 5.20 The most stable conformation of cis-4-tert-butylcyclohexyl bromide has the bromine substituent in an axial orientation. The hydrogen that is removed by the base is an axial proton at C-2. This hydrogen and the bromine are anti periplanar to each other in the most stable conformation H (CH3)C 5.21(a) 1-Heptene is CH2=CH(CH2)4CH, (b)3-Ethyl-2-pentene is CH_ CH=C(CH_CH3) (c) cis-3-Octene is CH, CH CH, CHCHCH (d) trans-1, 4-Dichloro-2-butene is CICH, CHCI Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website( f ) Two alkenes may be formed here. The more highly substituted one is 1-methylcyclohexene, and this is predicted to be the major product in accordance with Zaitsev’s rule. 5.18 Elimination in 2-bromobutane can take place between C-1 and C-2 or between C-2 and C-3. There are three alkenes capable of being formed: 1-butene and the stereoisomers cis-2-butene and trans- 2-butene. As predicted by Zaitsev’s rule, the most stable alkene predominates. The major product is trans- 2-butene. 5.19 An unshared electron pair of the base methoxide (CH3O) abstracts a proton from carbon. The pair of electrons in this C@H bond becomes the  component of the double bond of the alkene. The pair of electrons in the C@Cl bond becomes an unshared electron pair of chloride ion. 5.20 The most stable conformation of cis-4-tert-butylcyclohexyl bromide has the bromine substituent in an axial orientation. The hydrogen that is removed by the base is an axial proton at C-2. This hydrogen and the bromine are anti periplanar to each other in the most stable conformation. 5.21 (a) 1-Heptene is . (b) 3-Ethyl-2-pentene is . (c) cis-3-Octene is (d) trans-1,4-Dichloro-2-butene is C ClCH2 H C H CH2Cl C CH3CH2 H C CH2CH2CH2CH3 H CH3CH C(CH2CH3)2 CH2 CH(CH2)4CH3 Br H (CH3)3C (CH3)3C O H H C C CH3 H CH3 Cl CH Cl 3O H H2C C(CH3)2 CH3O 1-Butene cis-2-Butene CH2 CHCH2CH3 C C H3C H CH3 H trans-2-Butene C C H3C H H CH3 2-Bromobutane Br CH3CHCH2CH3 H3C I 1-Iodo-1-methylcyclohexane Methylenecyclohexane (disubstituted) CH2 CH3 1-Methylcyclohexene (trisubstituted; major product) STRUCTURE AND PREPARATION OF ALKENES: ELIMINATION REACTIONS 97 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website