The analogy between C=O and C(CN)2. Part 2.1 Structural properties of N,N-dialkylaminobenzamides and the analogously substituted 2-(phenylmethylene)propanedinitriles

Article abstract of DOI:10.1039/b105532c

The barrier to rotation around the carbon amino nitrogen bond in 2-[N,N-dimethylamino(phenyl)methylene]-propanedinitrile (4a), 2-[N,N-diethylamino(phenyl)methylene]propanedinitrile (4b), 2-[(phenyl)pyrrolidin-1-ylmethylene]propanedinitrile (4c), N,N-dimethylbenzamide (5a), N,N-diethylbenzamide (5b) and (phenyl)pyrrolidin-1-ylmethanone (5c) were determined using dynamic ¹H NMR spectroscopy. X-Ray crystal structures of 4a, 4b, 4c and 5a were determined, and quantum chemical calculations were carried out for 4a and 5a and for the transition structures for the rotation process of these two compounds. The barriers were generally lower than for the vinyl analogues 1 and 2. Although the calculated transition structures for 4a and 5a indicate some steric strain, the reduction of the barriers, especially for series 4, indicates that steric strain is more important in the ground state, thus raising its energy relatively more than for the transition state.

Full text of DOI:10.1039/b105532c

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The analogy between C᎐O and C(CN) . Part 2.1 Structural
᎐
2
properties of N,N-dialkylaminobenzamides and the analogously
substituted 2-(phenylmethylene)propanedinitriles
2
Hege Karlsen,a Per Kolsaker,*b Christian Rømmingb and Einar Uggerudb
a Amersham Health AS, Nycoveien 2, P.O. Box 4220 Nydalen, N-0401 Oslo, Norway
b Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway
Received (in Cambridge, UK) 25th June 2001, Accepted 12th December 2001
First published as an Advance Article on the web 23rd January 2002
The barrier to rotation around the carbon amino nitrogen bond in 2-[N,N-dimethylamino(phenyl)methylene]-
propanedinitrile (4a), 2-[N,N-diethylamino(phenyl)methylene]propanedinitrile (4b), 2-[(phenyl)pyrrolidin-1-yl-
methylene]propanedinitrile (4c), N,N-dimethylbenzamide (5a), N,N-diethylbenzamide (5b) and (phenyl)pyrrolidin-1-
ylmethanone (5c) were determined using dynamic 1H NMR spectroscopy. X-Ray crystal structures of 4a, 4b, 4c
and 5a were determined, and quantum chemical calculations were carried out for 4a and 5a and for the transition
structures for the rotation process of these two compounds. The barriers were generally lower than for the vinyl
analogues 1 and 2. Although the calculated transition structures for 4a and 5a indicate some steric strain, the
reduction of the barriers, especially for series 4, indicates that steric strain is more important in the ground state,
thus raising its energy relatively more than for the transition state.
crystal structure determination and quantum chemical
calculations.
Introduction
A few years ago we reported on the analogy in structural
properties of 4-(N,N-dialkylamino)-1,1-dicyanobuta-1,3-dienes
Results and discussion
(1) and 3-(N,N-dialkylamino)propenones (2) as studied by
dynamic 1H NMR, X-ray crystallography and quantum
chemical calculations on model compounds (Chart 1).1
Preparation of 4 and 5
The synthesis of the benzamides 5 was straight forward from
benzoyl chloride, while the 2-substituted propanedinitriles 4
were made via the triflate (trifluoromethanesulfonate) as
described in detail in the Experimental section (Scheme 1).
Chart 1 a: R1 = phenyl, R = Me; b: R1 = phenyl, R = Et; c: R1 = phenyl,
R2 = (CH2)4, atom numbering according to crystal structures.
Two important experimental results were obtained from
these studies. Firstly, the barriers to rotation around the C12–
N3 bond were almost identical within each series (≈ 1.0 kJ
molϪ1), but the barriers in 2 were about 10 kJ molϪ1 lower than
in series 1, indicating that the conjugation along the chain
N3–C1(O1) was more efficient in the latter series. This reduc-
tion of the barriers to rotation in series 2 relatively to 1 is also
corroborated by the crystal structure determinations. The N3–
C12 bond lengths are ≈0.01 Å longer and the C11–C12 bond
lengths are ≈0.01 Å shorter for series 2 than the corresponding
bond lengths in series 1, as expected if the conjugation is more
effective in the latter series. These trends were also indicated by
the quantum chemical calculations.
Scheme 1 Synthetic routes to 4 and 5.
Secondly, the lack of variations of the bond lengths and the
barriers to rotations by changing the amino alkylating groups
indicates that steric effects involving these groups are of minor
importance in both series. It then became interesting to see
how removal of the intermittent atoms C11 and C12 would
affect the structural properties as studied above. Therefore the
lower vinyl analogues 2-[N,N-dialkylamino(phenyl)methylene]-
propanedinitriles 4 and N,N-dialkylbenzamides 5 were syn-
Dynamic 1H NMR
The results of our determinations of the barriers to rotation for
the various substituted 4 and 5 are entered in Table 1. We found
it sufficient for our purpose to use the simplified method of
determining the coalescence temperature T c together with the
peak separation at slow exchange (∆ν) to estimate the barrier
using the well known equation [eqn. (1)2].
1
thesised and investigated by dynamic H NMR, X-ray single
404
J. Chem. Soc., Perkin Trans. 2, 2002, 404–409
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b105532c

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Table 1 Dynamic 1H NMR results for compounds 4 and 5 studied in N,N-dimethylformamide-d7, 0.1 molar solution
a, b
a, b
Cpd. T c(α) a/K
∆G#
∆νc/Hz
ν1/2 c/Hz
T c(β) a/K
∆G#
∆νc/Hz
ν1/2 c/Hz
Ref. valuesb
(α)
(β)
4a
4b
4c
5a
330
328
380
299
64.9 1.0
63.6 1.0
74.3 1.0
64.1 1.0
178.9
225.8
220.2
18.5
2.9
4.0
2.8
1.3
321
365
64.3 1.0
74.4 1.0
105.0
77.2
3.7
2.1
CDCl3: 64.4,3a 65.4,3b 65.5,3c 65.6,3d 66.03e
CD3CN: 63.5,3a 64.83d
CD3OD: 67.83e
5b
5c
304
324
61.5 1.0
69.1 1.0
77.5
23.2
3.1
3.3
291
61.8 1.0
23.6
2.1
CDCl3: 62.33f
CD3CN: 60.6,3f 62.63g
Not reported
n.f.d
a α = NCH3/NCH2–; β = –CH2–/–CH3. b In kJ molϪ1
due to small ∆ν.
.
c ∆ν, peak separation at slow exchange; ν1/2, averaged line width at slow exchange. d Not found
Table 2 Reduction in the barrier to rotation by removal of the C᎐C
the propanedinitrile group have completely different spatial
requirements.
᎐
double bond in compounds 1 and 2 (∆∆G#)a
Compound
Crystal structures
1a–4a
1b–4b
1c–4c
2a–5a
Ϫ0.4
2b–5b
2c–5c
Ϫ3.5
Unfortunately, only 5a of the amides was crystalline above
room temperature, a single crystal X-ray structure could be
obtained. ORTEP plots of structures 4a, 4b, 4c, and 5a are
presented in Fig. 2.
Difference
9.0
11.9
1.4
4.4
a In kJ molϪ1. Barriers for 1 and 2 are taken from ref. 1.
Selected structural data are given in Table 3 and dihedral
angles between nearly planar moieties are given in Table 4.
Some disorder was present in 4c where another conformer of
the five-membered ring is present in an amount of 25%. Data
for this conformer are disregarded. The crystal structures for
4a, 4b, 4c, and 5a indicate complete planarity along the X–N3
chain (X = C(CN)2), O–N1 chain for amide 5a, including the
first carbon atoms of the substituents at the amino nitrogen.
The phenyl group is almost perpendicular to this chain and to
the propanedinitrile group for the ethyl (4b) and pyrrolidine
(4c) compounds, and for the other two compounds (4a and 5a)
the dihedral angles (Table 4) are too high to account for any
conjugation effect between the phenyl group and the X-group
(O or C(CN)2). This absence of conjugation is corroborated by
the C4–C5 bond length (≈1.495 for cpds. 4 and 1.504 for 5a).4
These bonds and the C1–C4 bonds in 4 and the C4–O1 bond in
5a are almost identical with those in series 1 and 2,1 and C1–C4
in 4 are much longer than a formal double bond.
∆G‡ = RTc [23 ϩ lnT c /∆ν]
(1)
The estimated barriers to rotation for the benzamides 5a
and 5b (Table 1) correspond very well to those reported in the
literature,3 especially taking into account the expected solvent
effect.3c,3d,3f As mentioned in the introduction the barriers to
rotation were nearly identical within each series 1 and 2. This is
not the situation within series 4 and 5 where the values for the
barriers are quite scattered (Table 1). The obvious reason for
these differences must be of steric nature since the amino
groups in the latter two series are much closer to the rest of
the molecule. The steric requirement for the three amino sub-
stituents should be: methyl ≤ pyrrolidine < ethyl. The effect of
removal of the C᎐C bond on the barriers to rotation is given in
᎐
Table 2.
The process of rotation around the C–N bond is symmetrical
from one planar ground state to the other, and somewhere
along the route the amino nitrogen should be pyramidal
where resonance interaction with the X-group is minimised.
If in the transition state the phenyl is coplanar to the C(CN)2
The single bonds to the cyano groups for compounds 4 are
identical with the corresponding bonds in compounds 1,1 as are
the CN triple bonds, indicating that the electron withdrawing
effect of the cyano groups is inductive and that they do not
contribute in a resonance manner.5
or C᎐O groups, conjugation is reestablished as shown in
᎐
Fig. 1.
Quantum chemical calculations
Previous experience has shown us that the B3LYP/6–31G(d)
method is adequate for the purpose of estimating rotational
barriers in compounds of this type.1 In contrast to HF and
MP2 with the same basis set, B3LYP provides estimates of
the barriers in good accord with experiment. We found that the
calculated free energies of activation are approximately 10 kJ
molϪ1 lower than the corresponding experimental numbers.
One reason for the slight discrepancy is probably that the cal-
culations are conducted for the compound in vacuo, while the
experiments are carried out in solution.
The results of the present calculations are shown in Fig. 3
and 4 and Table 5. The structural parameters optimised for
4a and 5a are in excellent agreement with the X-ray crystallo-
graphic data. It is evident that both structures are sterically
congested in the neighbourhood of the amide bond. According
to the calculations the phenyl groups are 52 and 40 degrees
Fig. 1 Process of rotation around the C–N bond in 4 and 5.
The reduction of the barriers to rotation for 4 and 5 relative
to series 1 and 2 (except 2c–5c) as shown in Table 2 can be
interpretated as steric hindrance in the ground state where the
amino substituents are in the same plane as the X-group. This
strain is released in or near the transition state where the amino
nitrogen has pyramidal configuration. This indicates that the
transition state energy is influenced less by the change in struc-
ture going from series 1 to 4 and 2 to 5, and that the ground
state energy for the compounds with ethyl substituents suffers
the largest change. Somewhat surprising is the large difference
between the methyl and pyrrolidine substituents in propane-
dinitrile analogues, perhaps due to the freedom of rotation for
the methyl groups. The much smaller reduction of the barriers
for the oxygen analogues is certainly as expected as oxygen and
out of the C–C᎐C (4a) and C–C᎐O (5a) planes, respectively,
᎐
᎐
cf. Table 4. In addition, the C᎐C(CN) group is twisted by 20
᎐
2
degrees relative to the N(CH3)2 group. The implications of these
steric interactions is that full double bond conjugation cannot
J. Chem. Soc., Perkin Trans. 2, 2002, 404–409
405

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Table 3 Selected structural data for 4a, 4b, 4c, and 5a
Bond lengths/Å
4a
4b
4c
5a
C4–C5
C1(O1)–C4
C4–N3(N1 5a)
N3(N1 5a)–C11
1.492(2)
1.399(2)
1.338(2)
1.465(2)
1.470(2)
1.433(2)
1.428(2)
1.151(2)
1.152(2)
1.497(1)
1.406(1)
1.331(1)
1.474(1)
1.477(1)
1.426(1)
1.426(1)
1.161(1)
1.164(1)
1.497(1)
1.403(1)
1.306(3)
1.489(4)
1.468(7)
1.424(1)
1.426(1)
1.160(1)
1.160(1)
1.504(1)
1.242(1)
1.351(1)
1.456(1)
1.457(1)
N3–(C12 4a),(C13 4b),(C14 4c),(N1–C12 5a)
C1–C2
C1–C3
N1–C2
N2–C3
Bond angles/Њ
C1(O1)–C4–C5
C1(O1)–C4–N3(N1 5a)
C5–C4–N3(N1 5a)
117.8(1)
123.6(1)
118.6(1)
115.0(1)
126.9(1)
118.1(1)
117.8(1)
126.3(1)
115.8(1)
119.2(1)
122.0(1)
118.8(1)
Torsion angles/Њ
C1(O1)–C4–C5–C6
C1(O1)–C4–N3(N1 5a)–C11
C1–C4–N3–(C12 4a),(C13 4b),(C14 4c),O1–C4–N1–C12a (5a) Ϫ160.4(1)
Ϫ122.1(1)
Ϫ90.8(1)
3.9(1)
Ϫ178.1(1)
Ϫ87.9(1)
Ϫ2.9(4)
Ϫ178.5(3)
Ϫ125.7(1)
2.8(1)
Ϫ165.1(1)
16.2(2)
Fig. 2 ORTEP plots of 4a, 4b, 4c and 5a. Ellipsoids are shown at 50% probability. For 4c only the main conformer is shown.
be achieved in any of the two compounds, and the propanedi-
nitrile 4a appears to be more severely affected than the ketone
5a.
According to the B3LYP calculations the two rotational
barriers are 53 (65) and 51 (64) kJ molϪ1 (experimental value
in parenthesis). Similar differences were also found for the vinyl
analogues 1 and 2.1 This could be due to a solvent effect caused
by a more effective solvatisation of the ground state in the
rotation process, perhaps caused by a larger charge separation
in this state. Calculations of the dipole moments support such
a proposal (Table 6).
Upon C–N bond rotation to achieve the transition structures
(TS-4a and TS-5a, respectively), we have observed several
interesting structural features. Both transition structures have a
406
J. Chem. Soc., Perkin Trans. 2, 2002, 404–409

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Table 5 Energies from the quantum chemical calculations (B3LYP/6-
31G(d))
Table 4 Dihedral angles (Њ) between nearly planar moietiesa
Dihedral angle
Structure
Ea
Gb
∆Gc
4a
4b
4c
5a
4a
TS-4a
5a
TS-5a
6
TS-6
7
TS-7
Ϫ627.897914
Ϫ627.879005
Ϫ479.380411
Ϫ479.362719
Ϫ396.929303
Ϫ396.900558
Ϫ248.409183
Ϫ248.374623
Ϫ627.939209
Ϫ627.919210
Ϫ479.416872
Ϫ479.397497
Ϫ396.965462
Ϫ396.934592
Ϫ248.438262
Ϫ248.402896
0
52.5
0
50.9
0
81.1
0
1–2
1–3
2–3
67.2
59.5
33.8
88.5
88.9
12.1
86.0
88.1
2.2
58.9
45.8
9.0
a Plane 1, phenyl; plane 2, C4–NCC (the carbon atoms directly bonded
to N); plane 3, propanedinitrile group (5a: line C–O).
92.9
a Absolute energy at 0 K in Hartrees including zero point vibrational
energies. b Absolute Gibbs free energy at 298 K in Hartrees. c Relative
Gibbs free energies in kJ molϪ1
.
Table 6 Calculated dipole moments for ground and transition struc-
tures for 4a and 5a
Compound
4a
TS-4a
5a
TS-5a
µ/Debye
8.47
6.18
3.42
2.12
degree electronic or steric effects are responsible for the similar
barriers in the two compounds. In the conjugated systems
studied previously by us1 (Chart 1) rotation of the C–N bond in
the ketone requires less energy than in the propanedinitrile. If
the electronic effect was transferable from the previous system
to the present, this would indicate that the transition structure
is less sterically hindered than the minimum energy structure in
the case of the propanedinitrile.
To investigate this further, we performed calculations for
the analogous compounds 6 and 7, where the phenyl group
is substituted by hydrogen. It is highly interesting that for
this pair, the keto has a higher barrier for rotation than the
propanedinitrile. It therefore seems to be the case that the steric
hindrance of TS-4a is stronger than in TS-5a, since the
electronic effects affecting barrier heights should be rather
similar. The calculated barriers for 6 and 7 are in good agree-
ment with the experimental values which are determined to be
≈756 and ≈86 kJ molϪ1,7 respectively.
Fig. 3 Structural parameters for 4a, TS-4a, 5a and TS-5a as obtained
by quantum chemical calculations.
Experimental
General
Mps were measured on a Reichert Thermopan (Wien) apparatus
and are uncorrected. Infrared spectra were recorded on a
Nicolet Magna 550 FTIR spectrometer using an attenuated
total reflectance (ATR) ZnSe-plate for solid samples (unless
otherwise noted). High-resolution NMR spectra (1H and 13C)
were obtained using Bruker Spectrospin Avance DMX 200
and DMX 300 spectrometers where the reference compound
SiMe4 is software controlled; J-values are given in Hz. Ultra-
violet spectra were recorded using a Shimadzu UV-260
spectrophotometer, and mass spectra were obtained using a
Micromass Instrument ProSpec Q. Where dry conditions were
required, commercial solvents (FLUKA’s brand), dried to a
water content < 0.01%, stored under nitrogen over Molecular
Sieve, were used.
Fig. 4 Structural parameters for 6, TS-6, 7 and TS-7 as obtained by
quantum chemical calculations.
plane of symmetry, meaning that the N(CH3)2 moiety is per-
fectly perpendicular to the plane which consists of the rest
of the molecule. This allows for the phenyl groups to achieve
in-plane double bond conjugation with the respective double
Materials
The sodium salt of 2-[hydroxy(phenyl)methylene]propanedi-
nitrile (3) was prepared according to a slightly modified liter-
ature procedure.8 Benzoyl chloride (4.50 g, 32.5 mmol) and
malononitrile (2.12 g, 32.5 mmol) were dissolved in dichloro-
methane (50 ml) and cooled to 0 ЊC.
bond (C᎐C(CN) or C᎐O). However, a perpendicular transition
᎐
᎐
2
structure does not relieve steric strain by necessity. It is evident
from the indicated nonbonded contacts, that this is far from
being the case. As a consequence it is difficult to judge to what
J. Chem. Soc., Perkin Trans. 2, 2002, 404–409
407

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Benzyltriethylammonium chloride (TEBA, 0.75 g) in a 10 M
solution of NaOH (7.5 ml) was added dropwise while stirring.
After 15 minutes the precipitated solid was filtered off and
washed with dichloromethane (3 times) and diethyl ether
(3 times) and dried in a desiccator giving 5.9 g of 3, white
powder (94%). νmax/cmϪ1: 2210s (CN), 1527s, 1375s. δH(acetone-
d6): 7.3–7.4 (3 H, m), 7.6–7.7 (2 H, m). Spectroscopic data are in
accordance with literature values for the protonated salt.8
2-[N,N-Dimethylamino(phenyl)methylene]propanedinitrile
(4a), 2-[N,N-diethylamino(phenyl)methylene]propanedinitrile
9219 with Pt 100 sensor (DELTA OHM, 35030 Caselle di
Selvazzano, Italy).
X-Ray crystallographic analysis data for compounds 4a, 4b, 4c
and 5a
X-Ray data were collected on a Siemens SMART CCD dif-
fractometer10 using graphite monochromated Mo-Kα radi-
ation.† Data collection method: ω-scan, range 0.6Њ, crystal to
detector distance 5 cm. Data reduction and cell determination
was carried out with the SAINT and XPREP programs.10
Absorption corrections were applied by the use of the
SADABS program.11
The structure was determined and refined using the
SHELXTL program package.12 The non-hydrogen atoms
were refined with anisotropic thermal parameters; hydrogen
positions were located from difference Fourier maps and given
isotropic thermal parameters.
(4b),
and
2-[(phenyl)pyrrolidin-1-ylmethylene]propanedi-
nitrile (4c): the triflate of the above salt (3) was prepared
according to a literature procedure.9 To a solution of the
sodium enolate (2.00 g, 10.4 mmol for 4a and 0.53 g, 2.8 mmol
for 4b and 4c) in acetonitrile (65 ml for 4a and 20 ml for 4b
and 4c) was added trifluoromethanesulfonic anhydride (3.74 g,
2.19 ml, 10.4 mmol for 4a and 0.99 g, 0.58 ml, 2.8 mmol for 4b
and 4c), and the mixture was refluxed for 2 hours and cooled to
room temperature.
Dimethylamine (4.69 g, 104 mmol in 10 ml acetonitrile),
diethylamine (2.56 g, 35.0 mmol), or pyrrolidine (2.49 g,
35.0 mmol), was added as appropriate. After one hour, diethyl
ether was added and the mixture was washed with NaCl
solution, dried with MgSO4, and evaporated under reduced
pressure. The crude product was dissolved in dichloromethane
and filtered through a short SiO2 column. Recrystallization
from chloroform–pentane yielded 1.5 g 4a, white crystals
(63%), 0.13 g 4b, white crystals (21%), and 0.22 g 4c, light
yellow crystals (22%).
Crystal data for compound 4a. C12H11N3, M = 197.24, mono-
clinic, P21, a = 7.139(1), b = 7.955(1), c = 9.407(1) Å, β =
96.85(1)Њ, V = 530.43(6) Å3, Z = 2, Dx = 1.235 Mg mϪ3
,
µ = 0.077mmϪ1, T = 150(2) K, measured 5791 reflections in the
θ range 5.1–26.4Њ, Rint = 0.027. 180 parameters refined against
2096 F 2, R1 = 0.029 and wR2 = 0.070 for Io > 2σ(Io) and R1 =
0.033 and wR2 = 0.072 for all data.
Crystal data for compound 4b. C14H15N3, M = 225.29, mono-
clinic, P21/c, a = 9.883(1), b = 14.454(1), c = 8.915(1) Å, β =
95.36(1)Њ, V = 1267.96(5) Å3, Z = 4, Dx = 1.180 Mg mϪ3
,
µ = 0.072 mmϪ1, T = 150(2) K, measured 17827 reflections in
the θ range 2.1–37.8Њ, Rint = 0.018. 214 parameters refined
against 4430 F 2, R1 = 0.047 and wR2 = 0.107 for Io > 2σ(Io) and
R1 = 0.067 and wR2 = 0.141 for all data.
2-[N,N-Dimethylamino(phenyl)methylene]propanedinitrile
(4a). Mp 121–122 ЊC. νmax/cmϪ1: 2204s (CN), 2191m (CN).
δH(CDCl3): 2.12 (3 H, br), 2.83 (3 H, br), 7.3–7.4 (2 H, m),
7.4–7.5 (3 H, m). δC(CDCl3): 43.0, 44.2, 52.7, 116.6, 117.2,
128.4, 129.2, 131.6, 132.8, 171.5. MS (EI, 70 eV): m/z 197
ϩ
(100%, Mϩ ), 196 (92, [M Ϫ H] ), 156 (24). HRMS:
ؒ
Crystal data for compound 4c. C14H13N3, M = 223.27, mono-
clinic, P21/c, a = 8.458(1), b = 14.199(1), c = 10.533(1) Å, β =
Found: 197.095281, C12H11N3requires 197.095297 (0.1 ppm),
109.56(1)Њ, V = 1192.0(2) Å3, Z = 4, Dx = 1.244 Mg mϪ3
,
198.098859, C1113CH11N3 requires 198.098652 (Ϫ1.0 ppm).
µ = 0.076mmϪ1, T = 150(2) K, measured 24533 reflections in the
θ range 2.1–4.2Њ, Rint = 0.025. 235 parameters refined against
7112 F 2, R1 = 0.054 and wR2 = 0.147 for Io > 2σ(Io) and R1 =
0.073 and wR2 = 0.166 for all data.
2-[N,N-Diethylamino(phenyl)methylene]propanedinitrile (4b).
Mp 96–97 ЊC. νmax/cmϪ1: 2206s (CN), 2193m (CN). δH(CDCl3):
1.02 (3 H, br), 1.40 (3 H, br), 3.09 (2 H, br), 3.84 (2 H, br),
7.2–7.3 (2 H, m), 7.4–7.5 (3 H, m). δC(CDCl3): 13.7, 45.0, 48.6,
52.2, 116.5, 117.2, 127.4, 129.1, 130.8, 133.7, 169.0. MS (EI,
Crystal data for compound 5a. C9H11NO, M = 149.19, ortho-
rhombic, P212121, a = 6.631(1), b = 7.652(1), c = 16.303(1) Å,
ϩ
70 eV): m/z 225 (100%, Mϩ ), 224 (53, [M Ϫ H] ), 210 (35,
ؒ
[M Ϫ CH3]ϩ), 196 (43, [M Ϫ CH2CH3]ϩ). HRMS: Found:
225.126692, C14H15N3 requires 225.126598 (Ϫ0.4 ppm),
226.129710, C1313CH15N3 requires 226.129952 (1.1 ppm).
V = 827.21(11) Å3, Z = 4, Dx = 1.198 Mg mϪ3, µ = 0.079 mmϪ1
,
T = 150(2) K, measured 16518 reflections in the θ range
8.2–40.0Њ, Rint = 0.030. 144 parameters refined against 4831 F 2,
R1 = 0.040 and wR2 = 0.103 for Io > 2σ(Io) and R1 = 0.046 and
wR2 = 0.109 for all data.
2-[(Phenyl)pyrrolidin-1-ylmethylene]propanedinitrile (4c). Mp
199–199.5 ЊC. νmax/cmϪ1: 2206m (CN), 2192m (CN), 1549s.
δH(CDCl3): 1.7–1.8 (2 H, m), 2.0–2.1 (2 H, m), 3.15 (2 H,
Theoretical methods
3
3
t, J = 6.8), 4.00 (2 H, t, J = 6.9), 7.2–7.3 (2 H, m), 7.4–7.5
The program suite GAUSSIAN 9813 was employed for all
quantum chemical calculations. The hybrid density functional
theory method according to Becke14 incorporating the 6-
31G(d) basis set (B3LYP/6–31G(d))15 was used. All stationary
points were subject to complete geometry optimisation. The
optimised structures were checked for the correct number
of negative eigenvalues of the Hessian (the second derivative
matrix). Analytical force constants were computed at this stage
and the vibrational frequencies were obtained together with the
rotational constants. These molecular parameters were used
within the framework of the rigid rotor/harmonic-oscillator
approximation to calculate the absolute energies and Gibbs free
energies. Zero point vibrational energies were not corrected.
(3 H, m). δC(CDCl3): 24.5, 25.8, 50.7, 51.7, 53.9, 117.1, 117.3,
127.0, 129.2, 130.7, 134.0, 167.4. MS (EI, 70 eV): m/z 223
ϩ
(100%, Mϩ ), 222 (40, [M Ϫ H] ), 195 (25). HRMS: Found:
ؒ
223.110748, C14H13N3 requires 223.110948 (0.9 ppm),
224.113308, C1313CH13N3 requires 224.114302 (4.4 ppm).
N,N-Dimethylbenzamide (5a), N,N-diethylbenzamide (5b),
and phenylpyrrolidine-1-ylmethanone (5c). Benzoyl chloride was
allowed to react with the appropriate amine in acetonitrile
giving amines 5a, 5b, and 5c in good yields. Spectroscopic data
as expected for all three compounds.
NMR measurements
1
Variable-temperature H NMR spectra were obtained using a
Bruker Avance DMX 300 spectrometer. The probe temperature
was calibrated using a digital microprocessor thermometer HD
† CCDC reference numbers 168509–168512. See http://www.rsc.org/
suppdata/p2/b1/b105532c/ for crystallographic files in .cif or other
electronic format.
408
J. Chem. Soc., Perkin Trans. 2, 2002, 404–409

View Article Online
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