[earthnation112]

Just had a question about the Felkin‐Ahn model which is used to predict structure of the major diastereomer for nucleophilic additions to carbonyls. Before you draw the structure as the felkin-ahn model you need to draw the structure in its newman project, which newman projection conformation do you use? Since there are various conformations such as eclipsed, staggered, and gauche. Thanks

[phth]

Gauche with large group perpendicular to the carbonyl, smallest down low, and medium sized group next to the carbonyl. If there is a heteroatom bond attached to the α carbon, or possibility of hydrogen bonding, will the newmann projection be different?