SN2 mechanism

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 # 700

Write out a mechanism for the reaction below using curved arrows. Be sure to include formal charges. 

Problem # 677

Show a mechanism for the acid-catalyzed cyclization (condensation) of 1,4-butanediol.

Problem # 541

Rank the following compounds in order of decreasing reactivity with NaI in acetone. (1 = most reactive)

Problem # 537

Indicate the reagents necessary to carry out each transformation.

Problem # 534

Using curved arrows, draw the mechanism for the SN2 reaction below.