SUMMARY
A comparison of all the compounds studied and reported in the thesis
is done in the individual chapters, pointing out the similarities in their
structural parameters. These molecules belong to different groups or families
of organic compounds. Yet they exhibit interesting crystal packing features. In
all cases, intramolecular hydrogen bonds help for the stable conformation of
the molecules. In addition to this, intermolecular hydrogen bonds, non-bonded
interaction, C-H…π interaction, nitro-π interaction, π – π stacking interaction
and van der Waal’s force contribute to stabilise the molecules in three
dimensional crystal structure.
The compounds reported in Chapter II [IIa, IIb, IIc, IId, IIe (A,B,C) ]
belong to push pull butadiene family with the conformation that the systems
are conjugated due to partial double bonds and single bonds. In all the
molecules, the double bonds have a transoid geometry. In chapter III, there
are three different molecules [IIIa, IIIb, IIIc], one having planar conformation.
While IIIa is in enol form, IIIb and IIIc are in imino form. The molecules
reported in Chapter IV [IVa, IVb] are α-hydroxy methylated nitroalkenes with
comparable geometry where the nitroalkene moiety is planar. It is interesting
to note that both molecules show a layered arrangement. Chapter V gives the
overall geometry and molecular conformation of four different molecules [Va,
Vb, Vc, Vd]. The nitroalkene moiety is planar in all the molecules as in the
case of Chapter IV.
Strong intermolecular N-H…O hydrogen bonds are found in compounds
IIIa, Va, Vb, Vc and Vd, the parameters of these are shown in [Table A].
230
Table A.
Compound
D-H….A
H…A
D…A
D-H…A
(Å)
(Å)
(˚)
IIIa
N(1)-H(1)…O(2) 2.14(3) 2.973(3)
172
Va
N(1)-H(1)…O(1)
2.31
2.9411
131
Vb
N(1)-H(1)…O(1)
2.14
2.9406
154
Vc
N(1)-H(1)…O(2)
2.22
2.9954
150
Vd
N(1)-H(1)…O(2)
2.21
2.978
149
The C-H…N intermolecular hydrogen bonds occur in compounds IIb, IIc, and
IIe, the parameters are summarised in [Table B].
Table B
Compound D-H….A
H...A
D...A
D-H…A
(Å)
(Å)
(˚)
II b
C(10)-H(10B)…N(1)
2.60
3.465(5)
150.2
II c
C(10)-H(10B)…N(2)
2.49
3.387(8)
155
II e
C(10)C-H(10B)…N(2)B
2.61
3.537(5)
159
C(10)A-H(10C)…N(1)A
2.60
3.524(5)
160
C(10)B-H(10E)…N(1)C
2.61
3.524(5)
157
C(12)A-H(12A)…N(1)B
2.55
3.406(5)
154
C(12)B-H(12B)…N(2)A
2.55
3.406(5)
154
C(12)C-H(12C)…N(2)C
2.55
3.412(5)
154
231
Summary
The O-H..O hydrogen bonds found in IVa and IVb are summarised in
[Table C].
Table C
Compound
D-H….A
H....A
D....A
D-H…A
(Å)
(Å)
(˚)
IVa
O(3)-H(3)…O(3)
2.11
2.878(2)
157
IVb
O(3)-H(3)A…O(4)
2.33
3.038(2)
145.05
Weak C-H….O hydrogen bonds are the most commonly seen
intermolecular hydrogen bond in the molecules. Compounds IIc, IId, IIIa, IIIb,
IIIc, IVa, IVb, Va, Vb, Vc and Vd have C-H…O hydrogen bonds, their
parameters are summarised in [Table D].
232
Table D
H…A
D....A
D-H…A
(Å)
(Å)
(˚)
C(3)-H(3)…O(1)
2.59
3.509(6)
169
IId
C(11)-H(11C)…O(1)
2.56
3.335(7)
139
IIIa
C(9)-H(9)…O(2)
2.50(3)
3.307(4)
148(2)
IIIb
C(15)-H(15B)…O(3)
2.58
3.507(2)
161.8
C(3)A-H(3)A…O(2)B
2.57
3.4417
156
C(3)B-H(3)B…O(2)A
2.59
3.4485
154
C(1)B-H(1)B…O(2)A
2.59
3.5089
159
IVa
C(6)-H(6)…O(2)
2.55
3.4563
165.2
IVb
C(3)-H(3)…O(3)
2.33
2.710(2)
104.1
C(12)-H(12)…O(4)
2.44
3.1518
134
C(16)-H(16)…O(5)
2.54
3.383(2)
150.1
C(1)-H(1C)…O(2)
2.44
3.3658
162
C(16)-H(16)…O(4)
2.54
3.3300
142
C(19)-H(19)…O(2)
2.58
3.4163
150
C(20)-H(20)…O(4)
2.46
3.2345
141
C(18)-H(18)…O(1)
2.54
3.3130
140
C(19)-H(19)…O(2)
2.57
3.3945
148
C(20)-H(20)…O(4)
2.48
3.2055
135
Compound
D-H….A
IIc
IIIc
Va
Vb
Vc
Vd
π –π stacking interactions:
Novel π –π stacking interactions are observed in compounds IIa, IIb, IIc, IId,
IIe, IIIa, IVa, IVb, Va, Vb, Vc and Vd and helps in stabilisation of the
molecules as reported in Table E.
233
Summary
Table E:
Compound
Distance
IIa
between phenyl rings
5.316 Å
IIb
between phenyl rings
5.980 Å,
IIc
between phenyl rings
4.06 Å
IId
between phenyl rings
3.92 Å
IIe
between phenyl rings
4.60 Å
IIIa
between phenyl rings
5.28 Å
IVa
between thienyl rings
3.85 Å
IVb
between five-membered rings
3.709Å
between five & six membered rings
3.734Å
between six-membered rings
4.741 Å
between furan rings
4.857 Å
between six-membered rings
4.024 Å
between furan and phenyl rings
4.8464 Å
between six-membered rings
4.024 Å
between five-membered rings
3.995 Å
Vc
between six-membered rings
4.1214 Å
Vd
between six-membered rings
4.075 Å
Va
Vb
234
π – π interaction between dienes:
In addition to this, π - π stacking interactions between the double bonds
in the butadiene are observed in compound IId with the C(8) = C(9) acting as
the donor and C(12) = C(13) acting as the acceptor with an average distance of
4.09 Å between them.
C-H… π interactions:
In compounds IIb, IIc, IId, IIe, IIIb, IIIc, Vb and Vc, C-H… π interactions are
observed.
Table F :
Compound IId C-H group of the ester moiety and the aromatic ring
2.970 Å
Compound IIe C-H group of the dithiolan ring in A and the aromatic ring in B
3.00 Å
Compound IIIb C(11)-H and the phenyl ring C(2)…C(7)
2.78 Å
Compound IIIc C(11)-H of B and the phenyl ring C(2)…C(7) of A
2.73 Å
Compound Vb C-H group of the thiophene ring and a symm related thiophene ring 2.98 Å
Compound Vc C-H group of the phenyl ring and the furan ring
2.94 Å
Novel Nitro… π interactions:
It is very interesting that nitro…π interactions are found in compounds
IVa, IVb and Va, which are clearly tabulated as follows in Table G.
Table G:
Compound IV a
N atom of nitro group and the Cg of the thienyl ring
3.859 Å
Compound IV b
N atom of nitro group and the dioxol ring
3.699 Å.
Compound Va
N atom of nitro group and centroid of the phenyl ring
3.717Å.
235
Summary
Non-bonded interactions:
It is noticed that short non-bonded interactions are observed in compounds IIa,
IIb, IIIb, and Va. They are summarised in [Table H].
Table H:
Compound IIa
C(14)…O(1)
2.917(3) Å
Compound IIb
C(14)…O(1)
2.862(4) Å
Br(1) …N(1)
3.271(3) Å
Compound IIIb
C(4)…O(3)
3.386(2) Å
Compound Va
O(1)…O(3)
3.012(3) Å
O(1) …N(1)
2.941(2) Å
Thus, the above summarised hydrogen bonds and other interactions
help the molecules for stabilisation in three dimensional crystal structure.