Textbook: Brown 6th Ed. (2011)

Chapter 21: Benzene and the Concept of Aromaticity

Practice Problems (No matching mendel sets were found.)

Individual Problems

Problem # 580

Draw all resonance forms for each species.

For the anion and cation species, used curved arrows. For the radical species, use hooks.

Problem # 305

Rank each group of acids in order of decreasing acidity. (1 = most acidic)

Explain your reasoning. You will have to use more than one rule in your explanation (resonance, electronegativity, atomic radius, etc.). 

 

Problem # 581

Draw all products for the two reactions below.

The allylic alkene gives two products- the 1,2 product, and the 1,4 product. 

However, the benzylic alkene only gives the one product (analogous to the 1,2 product), instead of multiple products (like the 1,4 product, 1,6 product, and 1,8 product). Why is this the case?

Problem # 1281

Allylic and benzylic halides tend to undergo both SN1 and SN2 substitution reactions at a faster rate than their alkyl counterparts.

For example, both allyl chloride and benzyl chloride undergo SN2 reaction at a faster rate than propyl chloride. 

The same holds true for SN1 reactions: a 2° allyl or benzyl halide undergoes SN1 reaction faster than a 2° alkyl halide. Explain.

Problem # 582
 

Rationalize the follwing pKa values. Explain your answer in terms of the stabilites of the conjugates bases of each acid.

Note: the lower the pKa, the stronger the acid.

Problem # 583

Pyrrole is an example of a heteroaromatic compound: it contains a heteroatom (atom that is not carbon or hydrogen, such as N, O, S, etc.), and is aromatic.

Because pyrrole is aromatic, we should be able to draw many resonance forms- usually as many resonance forms as sides (in this case, five sides, so five resonane forms).

Draw all resonance forms for pyrrole. (I've started you off.)

Problem # 584

Imidazole (shown below) has two nitrogen atoms, N-1 and N-3. Which nitrogen is more basic?

To answer this problem, draw the product after each nitrogen protonates, and compare their stabilities. Explain your reasoning.