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>(2S4R)-4-Hydroxyproline(4-nitrobenzoate):Strong Induction of Stereoelectronic Effects via a Readily SynthesizedProline Derivative. Crystallographic Observation of a Correlationbetween Torsion Angle and Bond Length in a Hyperconjugative Interaction
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(2S4R)-4-Hydroxyproline(4-nitrobenzoate):Strong Induction of Stereoelectronic Effects via a Readily SynthesizedProline Derivative. Crystallographic Observation of a Correlationbetween Torsion Angle and Bond Length in a Hyperconjugative Interaction
(2S,4R)-4-Hydroxyproline(4-nitrobenzoate) was synthesized. The crystal structure revealed an exo ring pucker, with the nitrobenzoate pseudoaxial on the pyrrolidine envelope and antiperiplanar to Cβ and Cδ C–H bonds. The unit cell exhibited variation in Cδ–H/Cγ–O and Cβ–H/Cγ–O torsion angles, with a 15° increase in torsion angle (148° to 163°) observed to result in a 0.018 Å decrease in Cδ–H/Cγ–O bond length, consistent with favorable σC–H → σ*C–O hyperconjugative interactions increasing with greater orbital overlap.
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机译：合成了（2S，4R）-4-羟基脯氨酸（4-硝基苯甲酸酯）。晶体结构显示出exo环褶皱，硝基苯甲酸伪轴位于吡咯烷包膜上，与C β和C δ CH键成反平面。晶胞在C δ –H / C γ –O和C β –H / C γ –O扭转角，观察到扭转角增加15°（从148°至163°），导致C δ -H / C γ –O键长，与有利的σC–H→σ* C–O超共轭相互作用相符，且随着轨道重叠的增加而增加。
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