When ortho dibromobenzene is subjected to mono nitration?
Answers
Explanation:
1) NO+2 electrophile.
Yes
2) Benzene ring is attached to an activating group, so meta positions are enriched and electrophile has chances of attacking ortho/para positions.
The effect of the substituent in your example is probably similar to the effect of a methyl group (e.g. replacing a methyl hydrogen with a methoxy group won't have a big effect on the electron donating ability of the substituent). Look at the relative rates of nitration in the following figure.
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(image source)
We see that in toluene the ortho and para positions react 43 and 55 times (these two numbers are rather close) faster than in benzene, while reaction rate at the meta position changes little from benzene. This is consistent with the pi-donating ability of a methyl group adding electron density to the ortho and para positions making them more attractive to attack by an electrophile.
3) ortho position is more sterically hindered, hence para- major product and ortho minor product.
Look at the relative rate for the ortho position in t-butyl-benzene, here steric factors definitely play a role in slowing down attack at the ortho position. By comparison, the methyl group (and your substituent) is not very large and may slightly reduce the reaction rate at the ortho position in toluene (43 vs. 55 rather than both numbers being 55) or your example.
Another factor to consider is statistical in nature, there are two ortho positions, but only one para position. So, if everything else were equal, we would expect twice as much ortho product as para product.