Syntheses, crystal structure and ab initio calculations of two new phosphoric triamides

Article abstract of DOI:10.1016/j.molstruc.2005.04.010

The reaction of N-benzoylphosphoramidic dichloride with piperidine and 4-methylpiperidine lead to PhC(O)N(H)P(O)R₂ with R=piperidine (1) and R=4-methylpiperidine (2) as N-benzoyl-N′,N″-bis(piperidine) phosphoric triamide and N-benzoyl-N′,N″-bis(4-methylpiperidine) phosphoric triamide, respectively. The products have been characterized by ¹H, ¹³C, ³¹P NMR spectra, and by elemental analysis. The crystalline solid for (1) and (2) consists surprisingly of four and two independent molecules, respectively. There is a disorder in one amine group due to ring inversion in each conformer in compound 1. In the solid state, comparable magnitudes for the stabilization of the stable conformers for the more or less discrete molecules, the polarization effects, hydrogen bonding and the packing effects could be anticipated. The geometry of compound (1) optimized by density functional calculations at the B3LYP/6-31++G* (d,p) level, is in good agreement with data obtained from X-ray crystallography.

Full text of DOI:10.1016/j.molstruc.2005.04.010

Journal of Molecular Structure 750 (2005) 64–71
www.elsevier.com/locate/molstruc
Syntheses, crystal structure and ab initio calculations
of two new phosphoric triamides
b,
*
, C.O. Della Vedova , A. Anaraki Firooz ,
a
a,**
Kh. Gholivand
A. Madani Alizadehgana, M.C. Michelinic, R. Pis Diezb
aDepartment of Chemistry, Faculty of Science, Tarbiat Modarres University, P.O. Box: 4115-175, Tehran, Iran
bDepartamento de Quimica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 962, 47 esq. 115, 1900 LaPlata, Republica Argentina
cDipartimento di Chimica and Centro di Calcolo ad Alte Prestazioni, per Elaborazioni Parallele e Distribuite-Centro d’Eccellenza MURST,
`
Universita della Calabria, I-87030 Arcavacata di Rende, Italy
Received 23 February 2005; revised 21 April 2005; accepted 21 April 2005
Available online 4 June 2005
Abstract
The reaction of N-benzoylphosphoramidic dichloride with piperidine and 4-methylpiperidine lead to PhC(O)N(H)P(O)R2 with RZpiperidine
(1) and RZ4-methylpiperidine (2) as N-benzoyl-N0,N00-bis(piperidine) phosphoric triamide and N-benzoyl-N0,N00-bis(4-methylpiperidine)
phosphoric triamide, respectively. The products have been characterized by 1H, 13C, 31P NMR spectra, and by elemental analysis. The crystalline
solid for (1) and (2) consists surprisingly offour and two independent molecules, respectively. There is a disorder in one amine group due to ring
inversion ineach conformerin compound1. In the solid state, comparablemagnitudes for the stabilization of the stableconformers for the more or
less discrete molecules, the polarization effects, hydrogen bonding and the packing effects could be anticipated.
The geometry of compound (1) optimized by density functional calculations at the B3LYP/6-31CCG* (d,p) level, is in good agreement
with data obtained from X-ray crystallography.
q 2005 Elsevier B.V. All rights reserved.
Keywords: Phosphoric triamides; Disorder; Inversion; Density functional calculation; Crystallography
1. Introduction
information about the crystallographic structure of phos-
phoramidates can be considered scarce.
The very rapid development of the organophosphorus
chemistry during the last three decades has given rise to
the synthesis of many compounds bonded by phosphorus
and nitrogen [1–3]. Organophosphorus compounds with
the C(O)N(H)P(O) skeleton have attracted attention
because of their properties as ligands, antitumor agents
and urease inhibitors [4–6]. The existence of cyclic
amines in such molecules enables the existence of
different conformers due to the ring inversion and the
rotation about the P–N bond [1]. As far as we know,
Recently, compounds of this class with two independent
conformers in the unit cell have been reported [7,8].
A compound with three independent molecules in a unit
cell has been reported by Cain et al. for {(5R,4S)-N-Pr-
ephedrine}P(aS)[NH(SiMe3)] as a diazaphospholidine
heterocycle. [9]
In this work, we synthesized two novel phosphoramidate
of formula PhC(O)N(H)P(O)R2, with RZpiperidine (1) and
4-methylpiperidine (2). Surprisingly, X-ray diffraction data
for the compound (1) and (2) show the existence of four and
two independent molecules in the unit cell, respectively. As
far as we know, this is the first solid state structure of
phosphoramidate with four independent molecules in a unit
cell. The geometry of compound (1) has been optimized
by density functional calculations at the B3LYP/6-
31G*(d,p) level of approximation. These results confirm
X-ray experimental data.
*
**
Corresponding authors. Tel./fax: C542214714527.
Tel.: C98 21 8011001x3443.
E-mail addresses: gholi_kh@modares.ac.ir (K. Gholivand), carlosd@
quimica.unlp.edu.ar (C.O.D. Vedova).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.04.010

K. Gholivand et al. / Journal of Molecular Structure 750 (2005) 64–71
65
2. Experimental
2JHHZ12.72, 4H); 2.74–2.80 (multi. 4H); 3.64–3.68 (multi.
4H); 7.44–7.94 (multi, 5H, aromatic); 7.90 (s, 1H, NH); 13
C
2.1. Material and method
NMR (CDCl3), d (ppm): 32.01 (s, 2C); 32.03 (s, 2C(CH3));
35.42 (d, 2C 2JP–CZ4.94); 35.65 (d, 2C 2JP–CZ5.08); 45.80
2
All reactive and solvents were purchased from Merck.
1H, 13C and 31P NMR spectra were recorded on a Bruker
(Advance DRS) 500 MHz spectrometer. H, 13C and 31P
(d, 2C JP–CZ2.89); 46.65 (s); 128.78 (s); 129.66 (s,);
3
133.448 (s); 134.41 (d. JP–CZ8.55 Hz); 168.63 (s, CO);
31P {1H} NMR, d (ppm): 12.13 (s); 31P NMR, d (ppm):
11.81–12.27 (multi.) IR (KBr), n (cmK1): 725 (s); 837 (m);
955 (vs); 1059 (vs); 1105 (m); 1154 (s), 1190 (vs)(P(O));
1256 (m); 1445 (vs); 1668 (vs)(C(O)); 3060 (m) (NH).
1
chemical shifts were obtained in CDCl3 relative to TMS and
85% H3PO4 as external standards, respectively. IR spectra
were obtained using KBr pellets on a Shimadzu IR-60
model spectrometer. Elemental analyses were performed
using a Heraeus CHN–O– RAPID and melting point was
measured on Mettler FP 61 instrument.
2.3. Computational details
The conformational space of the molecules under study
was scanned using the molecular dynamics module of the
HyperChem package [11]. The MMC molecular mechanics
force field available in that package was used for the
simulations. The starting geometries were heated from 0 to
1000 K in 0.1 ps. Then the temperature was kept constant by
coupling the system to asimulated bath with a relaxation time
of 0.5 ps. After an equilibration period of about 5 ps, a 500 ps
long simulation was carried out saving the molecular
coordinates every 5 ps. The simulation time step was 0.5 fs.
The saved geometries were then minimized to an energy
2.2. Chemical syntheses
2.2.1. Synthesis of N-benzoylphosphoramidic dichloride
(compound A)
This compound was synthesized according to the
reported method of the literature. [10]
2.2.2. Synthesis of N-benzoyl-N0, N00-bis(piperidine)
phosphoric triamide (1)
This compound was synthesized from the reaction of
0.238 g, (1 mmol) compound A dissolved in 30 ml dry
acetonitrile with 0.34 g, (4 mmol) of piperidine. The amine
was added dropwise to a solution of compound A with
continuous stirring of the same and was cooled to K4 8C.
After a reaction time of 12 h, a white powder was obtained.
The solvent was evaporated in vacuum and the residue
washed with distilled water and dried at room temperature
(Yield: 90–98% with 98% purity). This compound was
recrystallized from concentrated solution of acetone at 4 8C.
Anal. Calc. for C17H26N3PO2: C, 60.89; H, 7.76; N,
˚
gradient smaller than 0.1 kcal/mol A, using the MMC
molecular mechanics force field. Another simulation at
1500 K was also performed to scan the potential energy
surface of the molecules as well as possible. The remaining
parameters of the simulation were kept similar to those of the
1000 K simulation.
The lowest-energy conformers found after the above
simulations were subject to further geometry optimizations
using the density functional theory [12]. With such a purpose,
the B3LYP hybrid exchange-correlation functional [13],
together with the 6-31CCG(d,p) basis set as implemented in
the GAUSSIAN 03 package [14], was used. All geometric
parameters were optimized without constraints.
1
12.53 found: C, 60.92; H, 7.80; N, 12.42.m.p, 198 8C. H
NMR (CDCl3), d (ppm): 1.56(multi, 12H); 3.18–3.23
(multi, 8H); 7.43–7.94 (multi, 5H, aromatic); 7.89 (s, 1H,
NH); 13C NMR (CDCl3), d (ppm): 25.52(s, 2C); 27.19((d,
The harmonic vibrational frequencies were then obtained
for the optimized geometries of the molecules under study in
thepresent work. Thefrequencieswerecalculated atthesame
level of theory as above. The importance of the vibrational
analyses is twofold. First, it enables the characterization of
3
2
4C), JP–CZ4.7 Hz); 46.81((d, 4C), JP–CZ2.7 Hz);
3
128.78(s); 129.65(s); 133.43 (d, JP–CZ8.5 Hz); 168.62(d,
CO, 2JP–CZ3.9 Hz); 31P {1H} NMR, d (ppm): 12.02 (s); 31
P
NMR, d (ppm): 11.75–12.2(multi.) IR(KBr), n (cmK1):
720(s); 836(m); 952 (vs); 1065(vs); 1106(m); 1156(s),
1203(vs)(P(O)); 1263(m); 1444(vs); 1667(s)(C(O));
3060(m)(NH).
N
O
O
Cl
Cl
N
P
P
N
N
2.2.3. Synthesis of N-benzoyl-N0,N00-bis(4-methylpiperidine)
phosphoric triamide (2)
O
O
H
H
+ Piperidin
Compound A
Compound (1)
This compound was synthesized in a similar way as (1),
using 4-methylpiperidine instead of piperidine. (Yield: 95–
98% with 98% purity). A crystalline solid was obtained
from a concentrated methanol/chloroform solution at 23 8C.
Anal. Calc. for C19H30N3PO2: C, 62.83; H, 8.26; N, 8.80
Me
Me
+ 4 -methylpiperidin
N
P
O
N
N
O
H
1
found: C, 62.90; H, 8.31; N, 8.69.m.p 215 8C. H NMR
(CDCl3), d (ppm): 0.91 (d, 6H, CH3, JHHZ6.22 Hz);
1.11–1.20 (multi. 4H); 1.45–1.50 (multi. 2H); 1.59 (d,
Compound (2)
Scheme 1. preparation of compounds (1) and (2).

66
K. Gholivand et al. / Journal of Molecular Structure 750 (2005) 64–71
Table 1
a given conformation as a true minimum on the molecular
potential energy surface. Secondly, if the conformation is
confirmed to be a minimum, then the calculated harmonic
frequencies are useful in the assignment of the experimental
vibrational data.
Crystallographic data for compounds 1 and 2
1
2
Empirical formula
Formula weight
Temperature
C17H26N3O2P
334.29
C19H30N3O2P
363.43
120 K
˚
0.71073 A
293(2) K
0.71073
Monoclinic
Cc
Wavelength
3. Results and discussion
Crystal system
Unit cell dimension
Triclinic
P-1
Piperidine and 4-methylpiperidine reacted with N-
benzoylphosphoramidic dichloride to form compounds 1
and 2, respectively (Scheme 1). The purity of the
compounds was checked by 1H, 13C, 31P NMR, IR,
elemental analyses and X-ray crystallography.
˚
˚
aZ9.330(2) A
aZ15.243(6) A
aZ908
aZ75.479(7)8
bZ18.054(3)‘A
bZ84.446(5)8
˚
˚
bZ10.895(5) A
bZ105.50(4)8
˚
˚
cZ22.021(5) A
cZ25.389(12) A
gZ908
gZ78.927(6)8
3
˚
3
˚
V
3519.4(13) A
4063(3) A
3.1. NMR study
Z
8
8
Radiation
Mo Ka
Mo Ka
Calculated density
Absorption coefficient
F(000)
1.262 Mg/m3
0.254 mmK1
1408
1.188 Mg/m3
0.152 mmK1
1568
Couplings between phosphorus and amidic nitrogen
nucleus have been observed in many phosphoramidic
compounds [7]. However, no such effect has been observed
for compounds 1 and 2. The 31P{1H} NMR spectra exhibit
only a single peak at 12.02 and 12.13 ppm for compounds 1
and 2, respectively. An interesting point in these molecules
Crystal size
0.27!0.22!
0.21 mm3
0.96–25.008
0.35!0.25!
0.15 mm3
1.66–22.008
q range for data
collection
Index ranges
K11%h%11
K20%k%21
K26%l% 26
22,875
K16%h%1
K11%k%1
K25%l%26
2648
is the coupling constants between the phosphorus and the
2
carbonyl carbon nucleus in compound 1 with JP–C
Z
3.77 Hz, which is absent in compound 2. Other differences
are insignificant in these molecules.
Reflections collected
Number of indep.
12,229 (0.1511)
2599(0.0208)
rflns(Rint
)
Absorption correction
Semi-empirical from
equivalents
None
3.2. X-ray crystal structure
Refinement method
Data/restraints/
Full matrix
Full matrix
2599/2/427
12,229/16/806
Single crystals of compound 1 and 2 were obtained as
air-stable colorless plates upon slow evaporation of a
concentrated solution of 1 in acetone and 2 in a mixture of
methanol and chloroform (v/v 5:1). Crystallographic data
for the structures reported in this paper have been deposited
in the Cambridge crystallographic data center as sup-
plementary publication numbers CCDC 240146(C17H26-
N3O2P) and 247021(C19H30N3O2P). Copies of the data can
be obtained free of charge on application to CCDC, 12
Union Road, Cambridge, CB2 1EZ UK (fax: C44 1223
336033; e-mail: deposit@ccdc.cam.ac.uk).
parameters
Goodness-of fit on F2
´
Final R ındices
0.856
1.031
R1Z0.0921,
wR2Z0.1998
R1Z0.3652,
wR2Z0.3874
0.840 and K0.1805 v
R1Z0.0899,
wR2Z0.2189
R1Z0.2272,
wR2Z0.3368
0.375 and K0.315 A
Enraf-Nonius CAD4
SHElXL-97
[FoO4d(Fo)],n
R indices (all data)
3
˚
Largest diff. peca
and hole
Measurement
Bruker SMART
1000CCD
Structure
SHElXL-97
determination
Crystallographic data for 1 and 2 are summarized
in Table 1. Selected bond lengths and angles are shown in
Table 2 for molecules 1 and 2. Crystallographic data show
Table 2
˚
Selected bond lengths (A) and angles (deg.) for the compounds 1 and 2
Bond lengths and
angles
Compound
1a
1b
1c
1d
2
2a
P(1)–N(1)
1.661(13)
1.642(14)
1.589(15)
1.472(13)
1.239(18)
103.7(7)
113.4(8)
104.7(8)
1.685(14)
1.619(17)
1.624(13)
1.425(12)
1.228(18)
106.0(7)
113.2(8)
104.2(9)
1.690(13)
1.631(14)
1.603(15)
1.463(11)
1.223(17)
112.7(7)
104.7(7)
104.2(8)
1.671(13)
1.614(13)
1.646(14)
1.406(12)
1.240(17)
115.2(7)
105.7(7)
103.2(8)
1.747(9)
1.653(14)
1.527(12)
1.444(10)
1.243(19)
106.4(6)
114.0(7)
103.9(7)
1.612(9)
1.658(11)
1.669(12)
1.470(11)
1.188(15)
108.0(6)
108.6(6)
104.7(7)
P(1)–N(2)
P(1)–N(3)
P(1)–O(1)
C(2)–O(2)
N(1)–P(1)–N(2)
N(1)–P(1)–N(3)
N(2)–P(1)–N(3)

K. Gholivand et al. / Journal of Molecular Structure 750 (2005) 64–71
67
Fig. 1. (1a), (1b), (1c) and (1d) show 4 independent conformers with ellipsoid probabilities of 50%.
˚
four independent molecules of compound 1 in the unit cell
(Fig. 1). Each form has disordered the amine group due to
ring inversion. The amines including N(2A), N(2B), N(3C)
and N(3D) atoms are disordered in (1a), (1b), (1c) and (1d)
conformers, respectively. Two independent forms have
been noted for compound 2. Experimental differences are
better described by comparison of corresponding torsion
angles for four conformers of 1 and two conformers of 2 that
are summarized in Table 3.
distance (1.39 (2) A) of 2 is shorter than a standard C–N
˚
single bond (1.47 A), but longer than a standard CaN
˚
double bond (1.28 A) [15] by considering the angles of
C–N–P in amine groups for compound 1 (nearly 1208) and
the angles of C(12)–N(2)–P(1), C(14)–N(3)–P(1), C(12A)–
Table 3
Selected torsion angles for compound 1 and 2 (deg.)
Torsion angle
Compound 1
Compound 2
Typical P–N single bonds are shorter than both typical
aminic P–N single bond lengths and amidic bond lengths for
the four conformers of 1, which are present in the unit cell.
Some difference between the P–N amidic bond length in
each conformer of compound 2 is also observed with values
O(1A)P(1A)N(1A)C(2A)
O(12B)P(1B)N(1B)C(2B)
O(1C)P(1C)N(1C)C(2C)
O(1D)P(1D)N(1D)C(2D)
O(2A)C(2A)N(1A)P(1A)
O(8B)C(2B)N(1B)P(1B)
O(2C)C(2C)N(1C)P(1C)
O(2D)C(2D)N(1D)P(1D)
O(1A)P(1A)N(1A)C(1A)
O(1)P(1)N(2)C(8)
K176(14)
177.5(15)
179.5
K175.9(4)
K8(3)
5(3)
–
–
–
–
–
–
˚
˚
of P(1A)–N(1A)Z1.612 A and P(1)–N(1)Z1.747 A,
respectively. For compound 2, the longest P–N bond in
K61(2)
K10(3)
–
–
–
˚
one of the conformers [P(1)–N(1)Z1.747(9) A] is worthy
K171.7(12)
K177.8(12)
K17(2)
K14(2)
–
of mention. This diminution of the bond order can be
ascribed to the interaction between the nitrogen atom and
the CaO group. Corroborating this point, the N(1)–C(1)
O(2A)C(1A)N(1A)P(1A)
O(2)C(1)N(1)P(1)
–
–

68
K. Gholivand et al. / Journal of Molecular Structure 750 (2005) 64–71
Fig. 2. The hydrogen bonding (1e) and the packing effect model (1f) for the compound (1) with ellipsoid probabilities of 50%.
N(2A)–P(1A) and C(14A)–N(3A)–P(1A) for compound 2
that are 120.6(12), 124.2(9), 121.4(10) and 129.7(13)8,
respectively, it can be concluded that, hybridization of the
nitrogen amine atom is pseudo sp2 (Fig. 1).
N(3)C(14)C(15)
C(16),
N(2)C(8)C(9)C(10),
N(2A)C(8A)C(9A)C(10A) and N(3A)C(14A)C(15A)-
C(16A) with values of 56.9(18), 56(2), K67(2) and 67(3)8,
respectively, confirm that an amine ring inversion should be
present in the second conformer.
Consideration of the packing models of the molecules
under study, 1, shows four types of hydrogen bonding and, 2,
two different types (see Figs. 2 and 3). Hydrogen bonding is
formed between the N–H proton of one conformer with the
phosphoryl oxygen atom of another one. Differences
between hydrogen bonding are listed in Table 4. Referring
to Table 2, differences between CaO bond lengths in
In the solid state, comparable magnitudes for the
stabilization of the stable conformers for the more or less
discrete molecules, the polarization effects, hydrogen
bonding and the packing effects could be anticipated
according to these results.
˚
compound 1 and 2 are only 0.01 and 0.055 A, respectively.
3.3. Theoretical calculations
Crystal structures show that the orientation of the PaO group
relative to CaO group is anti for both molecules. Torsion
angles C(8)C(9)C(10) C(13) and C(8A)C(9A)C(10A)-
C(13A) are K179.1(17)8 and K175.4(15)8, respectively, in
molecule 2 near to K1808, revealing that Me groups are in
equatorial position with respect to the amine rings.
Differences between torsion angles in compound 2,
The theoretical investigation of the species under study
afforded four stable conformers for molecule 1, in complete
agreement with the number of conformers experimentally
found. On the other hand, seven stable conformers were
obtained for molecule 2, in contrast with the two conformers
experimentally detected. It should be noted, however, that

K. Gholivand et al. / Journal of Molecular Structure 750 (2005) 64–71
69
Fig. 3. (2a) shows the structure of two conformers in compound (2) and their hydrogen bonding, (2b) depicts the packing effect model represented with
ellipsoid probabilities of 50%.
the calculations were carried out in vacuum, simulating a
low-pressure gas phase situation. It is then expected that
the free rotation of those methyl groups present in molecule
2 gives rise to a variety of conformers in the gas phase, not
all of them being stabilized in the solid state.
A careful comparison of experimental and calculated
geometric parameters indicates that the experimental values
are not well described in general by the theoretical values.
A comparison of the trends exhibited by the parameters,
however, allows us to identify the conformers as follows:
I is (1c), II is (1b), III is (1d), and IV is (1a). In other words,
(1c) is the lowest-energy conformation shown by the
molecule 1, with the (1b) conformer located at only
Table 5 shows the optimized geometric parameters
calculated for molecules 1 and 2. The total energies relative
to every lowest-energy conformer are also shown.

70
K. Gholivand et al. / Journal of Molecular Structure 750 (2005) 64–71
Table 4
Hydrogen bond for compound 1 and 2
˚
D(D–H) A
˚
˚
D–H
D(H/A) A
!DHA Deg.
D(D/A) A
A
Compound 1
N(1A)–H(1A)
N(1B)–H(1B)
N(1C)–H(1C)
N(1D)–H(1D)
N(1)–H(1A)
1.166
1.195
1.192
1.181
0.860
0.860
1.724
1.723
1.765
1.707
1.997
2.062
160.99
162.39
156.03
155.57
164.69
171.08
2.852
2.884
2.895
2.825
2.84
O(1D)
O(1C)
O(12B)
O(1A)
O(1A)
O(1)
Compound 2
Table 5
N(1A)–H(1AA)
2.91
Selected geometric parameters for the stable conformers calculated at the B3LYP/6-31CCG(d,p) level of theory for molecules 1 and 2
Parameter
Molecule 1
I (1c)
Molecule 2a
I
II(1b)
0.13
III(1d)
3.44
IV(1a)
4.52
II
III
IV
V
VI
VII
E
0.0
1.228
1.668
1.677
1.738
1.497
104.0
111.5
104.5
K175.2
27.4
0.0
1.224
1.681
1.681
1.737
1.490
104.0
104.6
102.9
K43.3
100.9
176.2
K25.3
K21.7
K47.2
1.30
1.227
1.703
1.671
1.741
1.489
105.3
97.0
1.74
1.229
1.669
1.686
1.724
1.493
110.7
104.1
102.1
K37.8
157.3
175.0
K33.3
2.06
1.228
1.682
1.690
1.714
1.494
115.3
103.1
98.6
2.53
1.227
1.667
1.693
1.741
1.496
104.7
112.1
104.7
33.0
4.52
1.229
1.695
1.677
1.737
1.493
104.7
97.0
5.83
1.228
1.695
1.667
1.738
1.497
105.3
104.4
111.9
K63.1
69.0
C–O
1.228
1.677
1.669
1.739
1.497
104.0
104.0
112.1
K67.7
74.7
1.226
1.672
1.703
1.740
1.489
105.4
108.1
97.1
1.224
1.682
1.682
1.737
1.490
104.0
102.9
104.7
25.0
P(1)–N(2)
P(1)–N(3)
P(1)–N(1)
P–O
N(2)P(1)N(3)
N(1)P(1)N(2)
N(1)P(1)N(3)
OP(1)N(2)C(9)
OP(1)N(2) C(13)
OP(1)N(3) C(14)
OP(1)N(2) C(18)
OC(2)N(1) P(1)
OP(1)N(1) C(1)
108.1
K83.0
50.8
108.9
58.5
165.3
18.4
173.2
K32.5
170.6
17.6
K177.3
K100.5
43.1
K162.2
K69.5
62.6
K76.5
K19.1
K78.1
64.4
K27.2
176.6
2.5
K50.6
83.8
K18.5
K165.3
4.7
151.9
K17.4
K140.1
140.9
K168.5
146.6
62.1
K10.9
K172.2
K6.0
K63.0
21.1
K164.5
K68.8
K163.5
K76.4
139.4
174.6
47.3
63.5
K139.3
Bond lengths are in angstroms, bond angles and dihedral angles are indegrees. Total energies relative tothe lowest-energy conformer are also given (E, in kcal/mol).
a
The geometric parameters of molecule 2 describe stable gas phase conformers and do not correspond to any of the two stable conformers found in the solid state.
0.13 kcal/mol above in energy. The other two conformers
lie slightly above in energy, 3.44 and 4.52 kcal/mol,
respectively, with respect to the (1c) conformer.
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but there are two in solid phase and seven in gaseous phase.

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