Chemistry Reference
In-Depth Information
C-3
δ
~ 11
In the
1
H-coupled spectrum, the peaks for C-1 and C-2 would be triplets, and the C-3
peak would be a quartet.
12.11
a.
Two; the methyl carbons are equivalent and the hydroxyl-bearing carbon is
unique.
b.
Five; the methylene carbons (
CH
2
) next to the carbonyl group are equivalent
as are the remaining two methylene (
CH
2
) carbons. The methane and the
exocyclic methyl group are unique. The carbonyl carbon is unique.
c.
Three; the methyl carbons are equivalent.
d.
Four; the molecule has an internal plane of symmetry passing through C-2
and the C(4)-C(5) bond.
12.12
The IR spectrum of 1-hexyne will show a band in the C
≡
C stretching frequency
region (2100-2260 cm
-1
) and in the
≡
C-H stretching frequency region (3200-3350
cm
-1
). These bands will not appear in the IR spectrum of 1,3-hexadiene, which will
show bands in the C
=
C (1600-1680 cm
-1
) and
=
C-H (3030-3140 cm
-1
) regions.
12.13
We use Beer's law:
A
=
ε
c l.
Rearranging the equation, we get:
c
=
A
÷ (
ε
l
)
= 2.2 ÷ (12,600 x 1) = 1.75 x 10
-4
mol/L
Note that ultraviolet spectra are often obtained on very dilute solutions.
12.14
Conjugation is possible between the two rings in biphenyl, but, in diphenylmethane,
the -
CH
2
- group interrupts this conjugation. Thus, for comparable electronic
transitions, biphenyl is expected to absorb at longer wavelengths.
12.15
Azulene. The blue color indicates that azulene absorbs light in the visible region of
the spectrum (400-800 nm). Naphthalene undergoes electronic transitions in the
ultraviolet region of the spectrum (314 nm). The longer the wavelength (nm), the
lower the energy of the electronic transition.
12.16
Alkanes have the molecular formula C
n
H
2
n
+2
. Therefore, for any alkane
n
(atomic wt. of C) + (2
n
+2) (atomic wt. of H) =
m/z
ratio of parent ion (M
+
)
In this case,
n
(12) + (2
n
+2)(1) = 114. Rearranging,
14
n
= 114 or
n
= 8
and the molecular formula of the alkane is C
8
H
18
. The intensity of the peak at
m/z
115 should be (1.1)(8) or 9% of the intensity of the peak at
m/z
114.
