Chemistry - STEREO ISOMERISM Question with Solution | TestHub
(a) What is the 'gauche effect'? Give examples.
(b) Draw the eclipsed and bisecting conformations of propylene (propene).
Options:
Answer:
Solution:
(a) In a conformational array A-B-C-D, where A and B are second-row electronegative atoms such as N, O or F, or unshared electron pairs, the often observed preference for the gauche (skew) conformation of A and B is called the gauche effect.
preferred conformation of FCH₂CH₂F (gauche effect) preferred conformation of H₂NNH₂ (gauche effect)
(b) Viewing propene along the C₂-C₃ bond, with the front sp² carbon carrying the =CH₂ group and H :
eclipsed conformation bisecting conformation
In the eclipsed conformation the C=C bond eclipses a C-H bond of the methyl group; in the bisecting conformation the C=C bond bisects an H-C-H angle of the methyl group.
