Much Ado About Aniline: Using resonance structures as part of your answer, expla

Question

Much Ado About Aniline: Using resonance structures as part of your answer, explain why the amino. NH2, group is: Strongly ring activating. An o-, p-director. [Note: It is not enough to use resonance structures from part "a" to "prove" part "b". One must show that o-: p-attack is faster, i.e. has lower EÄ (Delta Ga) by actually showing an electrophile, e.g. the generalized E+, attacking at the o-: m- & p-positions and. Using Hammond's Principle, explain why the o-, p-attacks are favored, i.e. are faster. {Where rate constant (k) = Ae"Ea/RT or e- Delta Ga/RT.}] Explain what polar (inductive, sigma -system) effect you would expect NH2 to have on the reactivity of the benzene ring. From your resonance structures of aniline in part "a" would you expect NH2to donate or remove electron density [e- p] from benzene's pi -system? That is, do your resonance structures tell you that NH2 would activate or deactivate benzene? Explain briefly. Based on your answer to parts "d" and "e" and the experimentally determined reactivity of aniline, how strong is NH2's resonance (pi -system) effect versus its polar effect? Explain. What must be the hybrid state of Nin aniline? Why? How do your resonance structure from part "a" help support this conclusion?

Explanation / Answer

a)

bcozas nitrogen is less eletronegative than oxygen so the delocalisation of lone pair eletron to the benzene ring is more in case of amine compare to hydroxyl group

b)

Directing Groups

The rate of substitution on a benzene ring is affected by what groups are already on the benzene ring. Those groups which lower the rate of electrophilic substitution is calld an activating group. Any substituent that lowers the rate (from benzene) of substitution is called a deactivating group.

An important thing to know about substitution reactions on benzene is that you will NEVER get exactly what you want. You always get a mixture of what you want (a mixture of ortho/para/meta groups), and you must then use methods to separate the stuff you don't want. For instance, you may want to substitute a nitro group para from the the methyl group in the toluene. Once you have finished with the substitution reaction, only 37% of the final product will have the nitros in the para position. About 59% will have the nitro in the ortho position, while 4% will have the nitro in the para group.

So when you plan out your substitutions, note what is on the benzene ring and remember that these groups will DIRECT whatever substitution you want to a certain position.

Ortho-Para Directors Meta Directors

-NH2 (amino)

c)

Hammond principle:

When the transition state is closer in energy to the products rather than the starting materials, those factors that stabilize the products will stabilize the transtion state to a greater degree.

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