CHAPTER 7: Question 4
2D Explanations
The sequence of the answers is from left to right along each row
in turn.
Applying the CIP rules to the three substituents attached to the carbonyl
carbon atom gives the sequence O > C > H (rule 1). The priorities of the
groups decrease in an anti-clockwise direction as shown below, so the front
face is the si-face.
Applying the CIP rules to the three substituents attached to the carbonyl
carbon atom gives the sequence O > C > H (rule 1). The priorities of the
groups decrease in a clockwise direction as shown below, so the front face
is the re-face.
Only the lower end of the alkene need be considered since there are
two identical substituents attached to the upper end of the alkene. Applying
CIP rules 1-3 to the three substituents attached to the lower end of the
alkene gives the result shown below. Note that the =CH2 is treated
as -CH2(C) (rule 3) and so has a higher priority than the methyl
group but lower than the tert-butyl group. The priorities of the groups
decrease in a clockwise direction, so the front face of the alkene is the
re-face.
Considering first the left side of the C=N. CIP rules 1 and 2 allow
the priorities of the three substituents to be assigned as N > Ph > CH3.
These decrease in an anti-clockwise direction, so the front face of the
left side of the C=N bond is the Si-face. To apply the CIP rules to the
right side of the imine bond, the lone pair is first added to the nitrogen
atom and is treated as a substituent. The priorities are then O > C > lone
pair, and these decrease in an anti-clockwise direction, so the front face
is again the si-face.
Considering first the left side of the C=N. CIP rules 1 and 2 allow
the priorities of the three substituents to be assigned as N > Ph > CH3.
These decrease in an anti-clockwise direction, so the front face of the
left side of the C=N bond is the Si-face. To apply the CIP rules to the
right side of the imine bond, the lone pair is first added to the nitrogen
atom and is treated as a substituent. The priorities are then O > C > lone
pair, and these decrease in a clockwise direction, so the front face of
the right side of the C=N bond is the re-face.
Considering first the left side of the C=C. CIP rules 1-2 allow the
priorities of the three substituents to be assigned as =CBrCl > Ph > Et.
These decrease in an anti-clockwise direction, so the front face of the
left side of the C=C bond is the Si-face. Only CIP rule 1 is need to assign
the priorities of the three substituents attached to the right side of
the C=C as Br > Cl > C. These decrease in a clockwise direction, so the
front face of the right side of the alkene is the re-face.
Only the left side of the C=O need be considered since the oxygen atom
has two lone pairs. CIP rules 1 and 2 allow the priorities of the three
groups around the carbonyl carbon to be assigned as shown below, and these
decrease in a clockwise direction, so the front face is the re-face.
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