Organic Chemistry I

Strong (good) nucleophile:
OH
–
, RO
–
(small alkoxide), RS
–
(thiolate), N
3
–
(azide), CN
–
(cyanide), Cl
–
, Br
–
, I
–
(halide),
RCO
2
–
(carboxylate), RNH
2
(amine)
Weak (poor) nucleophile
: ROH, H
2
O,
t
-BuO
–
With the structure of nucleophiles being so diverse, S
N
2 reaction can be used to synthesize the compounds with a
variety of functional groups, as shown here.
7.3 Other Factors that Affect SN2 Reactions | 251

---

Figure 7.3b Functional group interconversions via SN2 reactions
Examples
252 | 7.3 Other Factors that Affect SN2 Reactions

---

Exercises 7.2
Show reaction mechanism of the above reactions.
Answers to Practice Questions Chapter 7
7.3 Other Factors that Affect SN2 Reactions | 253

---

7.4 SN1 Reaction Mechanism, Energy Diagram and
Stereochemistry
S
N
1 Reaction Mechanism
The reaction between
tert
-butylbromide and water proceeds via the SN1 mechanism. Unlike S
N
2 that is a single-step
reaction, S
N
1 reaction involves multiple steps. Reaction: (CH
3
)
3
CBr + H
2
O 
→
(CH
3
)
3
COH + HBr
254 | 7.4 SN1 Reaction Mechanism, Energy Diagram and
Stereochemistry

---

In
step 1
, C—Br bond breaks and Br departs with the bonding electron pair to produce a tertiary carbocation and
bromide anion Br
–
. This step only involves a highly endothermic bond-breaking process, and this is the slowest step in
the whole mechanism. In multiple-step mechanism, the overall reaction rate is determined by the slowest step, such
step is therefore called the