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P. G. Jones – P. Ku s´ · Secondary Interactions in Bromomethyl-substituted Benzenes
˚
a
Table 2. Hydrogen bonds (A and deg) for compounds 1 – 5 .
Com-
H
D–H···A
d(H···A) d(D···A) ∠(DHA)
pound bond no.
b
1
1
2
3
4
C4–H4B··· Br#1
C4–H4A··· Br#2
3.04
3.13
3.09
3.15
3.914(2)
4.077(2)
4.078(2)
3.956(2)
138
146
152
132
g
C2–H2··· Br#3
g
C2–H2··· Br#4
2c
3d
1
2
3
4
C7–H7B··· Br1#1
2.96
2.96
3.01
3.02
3.915(9)
4.020(9)
3.846(9)
3.928(8)
148
168
135
142
C8–H8A··· Br2#2
g
C5–H5··· Br2#3
g
C5–H5··· Br1#4
Fig. 8. C–H···π interaction in compound 3 (see text). Dis-
h
1
2
3
4
5
C4–H4A··· Br#1
2.85
3.07
3.05
2.71
2.84
3.653(2)
3.973(2)
3.726(2)
3.72
131
141
121
156
163
˚
tances are in A.
g
C3–H3··· Br#2
g
C3–H3··· Br#3
acceptors than π electrons, and thus no strong hydro-
gen bonds of the type C–H···π are observed in these
i
C4–H4B··· [f070]#4
C2–H2··· Midpt
3.89
ꢀ
˚
(
C3–C3 )#4
compounds (the contact H8B···π 2.88 A in 2 via a
4e
1
2
3
4
5
6
C4–H4B··· Br1#1
C5–H5A··· Br1#2
C5–H5B··· Br1#3
C2–H2··· Br2#4
C4–H4A··· Br2#4
2.87
2.94
3.10
3.11
3.02
3.15
3.940(3)
3.880(3)
3.958(3)
4.066(3)
3.862(3)
3.958(3)
172
146
137
148
135
132
y axis translation, identifiable but not explicitly shown
in Fig. 7, has a very narrow angle of 116 ).
g
◦
For the ortho derivative (3), the space group Fdd2
leads, as so often, to a complex packing diagram. Fur-
thermore, the principles that seemed so logical for 1
and 2 are no longer valid. Of the two methylene
hydrogen atoms, one is involved in an intramolecu-
lar C–H···Br interaction (1). There are no significant
g
C5–H5A··· Br2#5
5f
1
2
3
4
5
6
7
8
9
C7–H7A··· Br1#1
j
3.10
2.98
2.93
3.05
3.22
2.94
2.97
2.90
2.86
3.672(3)
4.046(4)
3.541(3)
3.571(3)
4.238(3)
3.975(4)
3.848(3)
3.804(3)
3.909(3)
113
170
116
110
158
160
138
141
165
C10–H10B··· Br1#2
j
C7–H7A··· Br3#3
g
C9–H9B··· Br3#4
˚
g
Br···Br contacts (the shortest is 4.46 A), and the only
C9–H9B··· Br2#7
C10–H10A··· Br3#2
intermolecular C–H···Br hydrogen bond is a three-
centre system (2, 3) from H3. Hydrogen atoms H2
and H4B form short C–H···π contacts (4, 5) to an ad-
jacent molecule (Fig. 8). The overall packing is a three-
dimensional linkage of chains of molecules parallel to
the polar z axis, best seen as a stereo view (Fig. 9).
j
C7–H7A··· Br4#5
C8–H8B··· Br4#6
C9–H9A··· Br4#7
a
˚
b
All C–H bond lengths normalized to 1.08 A; symmetry trans-
formations used to generate equivalent atoms: #1 x, y + 1, z; #2 x,
c
1
1/2−y, −1/2+z; #3 −x, 1−y, 1−z; #4 x, 1/2−y, −1/2+z; symme-
try transformations used to generate equivalent atoms: #1 x, −1+y,
In the tetrasubstituted compounds 4 and 5, it is again
the bromomethylene group that plays the major role
in the packing (there are no significant H···π interac-
tions). In compound 4 they combine (via translation
z; #2 1/2 − x, 1/2 + y, 1/2 − z; #3 1 − x, 1 − y, 1 − z; #4 11/2 − x,
d
−
1/2+y, 1/2 −z; symmetry transformations used to generate equiv-
alent atoms: #1 1 − x, 1− y, z; #2 x, y, −1+ z; #3 3/4 − x, −1/4 + y,
e
−
3/4 + z; #4 −1/4 + x, 3/4 − y, 1/4 + z; symmetry transformations
used to generate equivalent atoms: #1 x, 1/2−y, −1/2+z; #2 x, 1/2−y, and glide planes) to form a layer structure parallel to
1
/2 + z; #3 −x, 1/2 + y, 11/2 − z; #4 1 − x, −1/2 + y, 11/2 − z; #5 x,
the yz plane (Fig. 10). The molecules lie approximately
f
1
1/2 −y, 1/2 +z; symmetry transformations used to generate equiv-
◦
perpendicular (74 ) to the layer, the top and bottom
of which contain the bromine atoms, and which is ac-
alent atoms: #1 11/2 − x, 1/2 + y, 1/2 − z; #2 1− x, 1− y, 1− z; #3 x,
1
1
+ y, z; #4 1/2 − x, 1/2 + y, 1/2 − z; #5 1− x, 2− y, 1− z; #6 1/2 + x,
g
1/2 −y, −1/2 +z; #7 1/2 −x, −1/2+y, 1/2−z; components of three- cordingly quite thick. The predominant interactions are
h
i
centre system; intramolecular; π denotes the centroid of the six-
membered ring; components of four-centre system.
˚
a very short Br···Br contact (1) of 3.50 A, which is
j
however type I in terms of its angles [6], and the two
shortest C–H···Br hydrogen bonds (1, 2). Two further
bond (1) within the layer; the hydrogen bond from the H bonds from C5 (3, 6) are observed within the layer
methylene group at C8 (2) is directed to a neighbouring (one as a weak component of a three-centre interac-
layer. A natural explanation for the observed hydrogen tion from H5A; cf. Table 2) but have been omitted
bonding behaviour of the bromomethyl groups is that from Fig. 10 for clarity. The other three intermolecular
the inductive effect of bromine increases the acidity Br···Br contacts and the remaining H bonds connect
of methylene hydrogen atoms, thereby making them neighbouring layers.
more attractive donors compared to hydrogen atoms of
the benzene ring. Likewise, bromine atoms are better bromomethyl groups leads to a complex three-dimen-
For compound 5, the presence of four independent
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