COOH CH3 H OH 旋转180 HO 一H CH3 COOH 旋转I8 COOH H H OH CH3 COOH CH3 OH 旋转0COOH H OH COOH CH3 旋 转180 HO H 旋转180 CH3 。 。 COOH H OH CH3 COOH H OH 旋 转90 旋 转90 CH3 。