CONFORMATIONS OF ALKANES AND CYCLOALKANES 51 (b) The o-H proton may be anti to one N-H proton and gauche to the other(left)or it may gauche to both(right) H H 3.16 Conformation (a) most stable; all its bonds are staggered. Conformation(c)is the least stable all its bonds are eclipsed 3. 17 (a) First write out the structural formula of 2, 2-dimethylbutane in order to identify the substituent groups attached to C-2 and C-3. As shown at left, C-2 bears three methyl groups, and C-3 bears two hydrogens and a methyl group. The most stable conformation is the staggered one shown at right. All other staggered conformations are equivalent to this one Sight along this bond CH/H CH H 3C CH H (b) The constitution of 2-methylbutane and its two most stable conformations are shown. Sight along this bond. C-C -CH H H CH Both conformations are staggered. In one(left), the methyl group at C-3 is gauche to both of the C-2 methyls. In the other (right), the methyl group at C-3 is gauche to one of the C-2 methyls and anti to the other. (c) The hydrogens at C-2 and C-3 may be gauche to one another(left), or they may be anti (right). CH H3 HC H HC-C-C--CH3 CH Sight along this bond 3.18 The 2-methylbutane conformation with one gauche CH3... CH3 and one anti CH3.CH3 rela- tionship is more stable than the one with two gauche CH3..CH3 relationships. The more stable conformation has less van der waals strain CH H3C. HH C H More stable Less stable Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website(b) The OGH proton may be anti to one NGH proton and gauche to the other (left) or it may be gauche to both (right). 3.16 Conformation (a) is the most stable; all its bonds are staggered. Conformation (c) is the least stable; all its bonds are eclipsed. 3.17 (a) First write out the structural formula of 2,2-dimethylbutane in order to identify the substituent groups attached to C-2 and C-3. As shown at left, C-2 bears three methyl groups, and C-3 bears two hydrogens and a methyl group. The most stable conformation is the staggered one shown at right. All other staggered conformations are equivalent to this one. (b) The constitution of 2-methylbutane and its two most stable conformations are shown. Both conformations are staggered. In one (left), the methyl group at C-3 is gauche to both of the C-2 methyls. In the other (right), the methyl group at C-3 is gauche to one of the C-2 methyls and anti to the other. (c) The hydrogens at C-2 and C-3 may be gauche to one another (left), or they may be anti (right). 3.18 The 2-methylbutane conformation with one gauche CH3 . . . CH3 and one anti CH3 . . . CH3 rela￾tionship is more stable than the one with two gauche CH3 . . . CH3 relationships. The more stable conformation has less van der Waals strain. CH3 H3C CH3 H H H CH3 H3C CH3 H H H More stable Less stable CH3 H3C CH3 CH3 H H CH3 H CH3 CH3 H3C H H3C C C CH3 CH3 CH3 H H Sight along this bond. CH3 CH3 H H3C H H CH3 H CH3 H3C H H H3C CH C C 3 H CH3 H H Sight along this bond. CH3 CH3 CH3 H3C H H H3C CH C C 3 CH3 CH3 H H Sight along this bond. N H O H H N H H O H CONFORMATIONS OF ALKANES AND CYCLOALKANES 51 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website