Page 278 - Mechanism and Theory in Organic Chemistry

Problems 265

nor must the triplet necessarily add with loss of stere~chemistry.~~~ Table 5.10
presents the data. It will be noted that, with the exception of dicyanomethylene,
loss of stereochemistry is not complete in triplet additions. The rates of spin
inversion and bond rotation must be of comparable magnitudes. We discuss this
point further in Section 12.1. Stereochemistry of the concerted additions is also
considered further in Section 12.1. Carbenoids add stereo~pecifically,~~~ but
since free carbenes are not involved, the singlet-triplet considerations do not
apply.

PRoaE: that the simple limiting SN1 mechanism predicts the kinetic behavior
Equation 5.4, p. 214.
Explain the rate ratio for compounds 1 and 2 estimated for limiting solvolysis.
H3C\ (CH3)3C\
H-C-OTs CHOTS
/
H3C (~~313~'
1 2
Relative rate
(estimate) : 1 1 o5
3. Explain the rate ratio for compounds 3 and 4 estimated for limiting SN1
solvolysis by correcting the cyclopropyl system for anchimeric assistance which
occurs when the ring opens.

3 4
Relative rate
(estimate) : 1 10-lo
4. Solvolysis rates of isopropyl tosylate and 2-adamantyl tosylate (28, p. 243) in
80 percent ethanol are measured with and without added azide. Define rate enhance-
ment, R.E., as the ratio of rate with azide to rate without, and designate by f,,, the
fraction of alkyl azide in the product. Explain the significance of the fact that the iso-
propyl results fit the equation
1
I-- ~ R N ~
R.E.
while the 2-adamantyl results do not.
Explain why the carbene 5 does not react with cyclohexene in the manner of
ordin 2 carbenes, but does react with dimethyl fumarate (6) and maleate (7) to yield
y
spiropentanes (8).

lTa See note 141(b), p. 256 and note 171.
lT3 G. L. Closs and L. E. Closs, Angew. Chem. Znt. Ed., 1, 334 (1962).