INVESTIGATION OF MOLECULAR INTERACTION BETWEEN PHENYLACETYLENE AND HEXAMETHYLPHOSPHORIC TRIAMIDE BY 13 C NMR T 1 RELAXATION TIME STUDIES AND AB INITIO QM CALCULATIONS | Siahaan | Indonesian Journal of Chemistry 21668 40754 1 PB

Indo. J. Chem., 2007, 7 (3), 273-277

273

INVESTIGATION OF MOLECULAR INTERACTION BETWEEN PHENYLACETYLENE AND
HEXAMETHYLPHOSPHORIC TRIAMIDE BY 13C NMR T1 RELAXATION TIME STUDIES AND
AB INITIO QM CALCULATIONS
Parsaoran Siahaan1,*, Cynthia L. Radiman2, Susanto Imam Rahayu2, Muhamad A. Martoprawiro2,
and Dieter Ziessow3
1

2

Chemistry Study Program, Faculty of Mathematics and Natural Sciences,
Jl Ganesha 10 Bandung Indonesia

Inorganic and Physical Chemistry, FMIPA ITB, Jl Ganesha 10 Bandung Indonesia
3

Stranski Laboratory for Physical and Theoretical Chemistry TU Berlin, Germany
Received 26 May 2007; Accepted 18 September 2007

ABSTRACT
Intermolecular interactions and molecular translational and rotational mobility are key factors in molecular
material sciences, e.g. liquid crystals. One of the important substructures is given by phenylacetylene, Ph-CCH. Its
rotational behavior in its pure form and in high dilution in hexamethylphosphoric triamide OP[N(CH 3)2]3 (HMPA) has
13
been studied by means C NMR T1 relaxation times at ambient temperature as measured by the inversion recovery
method. HMPA is an exceptional solvent in that is has a quite large dipole moment but comparatively low relative
dielectricity constant. From the molecular shape Ph-CCH is expected to exhibit anisotropic rotational diffusion
which in fact can be deduced from the measured set of T 1 values of the ortho, meta and para carbon nuclei in the
neat liquid as well as in the HMPA solution. This expected result rules the dominance of a linearly molecules pair PhCCH…HMPA along their dipole moment axes as anticipated in view of the large HMPA dipole moment. In order to
conform with the T1 data, a linear arrangement of Ph-CCH via the interaction between its weakly acidic H-atom with
negatively charge O-atom of HMPA molecules seems to lead to such an anisotropic rotational motion. This
hypothesis is supported by ab initio QM calculations which come out with higher interaction energy for linear
orientation than other geometries. These ab initio calculations were performed with the basis set of RHF/6-31G(d)
for the single molecules of Ph-CCH and HMPA as well as for their various geometries of the molecules pair.
Molecular dynamics simulations need to be performed for further confirmation.
Keywords: Relaxation Times, HMPA, pheylacetylene, ab initio, intermolecular interaction, rotational diffusion
INTRODUCTION
To increase the beneficiaries of the information

involved in NMR spectroscopy whether as images (in
magnetic resonance imaging, MRI) or spectra it can be
done by understanding of spin-lattice and spin-spin
relaxation times. The mainly mechanism one of spin13
1
lattice relaxation is
C- H dipole-dipole or dipolar
interaction. So, molecular dynamics properties of local
and the whole structure that partly determine the
properties of the system are obtained by NMR method,
which are known through the information that is
indicated on the reorientation behaviour of dipole-dipole
13
1
vector of nuclear spin in which one of them is C- H
dipole-dipole. That information included in a data which
13
is called C NMR T1 relaxation times. Measurement of
spin-lattice relaxation times can give the information of
molecular dynamics. Because of the interaction can

affect molecular dynamics, then this interaction can also
13
1
be known from
C- H dipole-dipole orientation of
nuclear spin. If two or more of molecule interact, it will
form what is called paired-molecule. It can be between
solute-solute, solute-solvent, and solvent-solvent. The
* Corresponding author.
Email address : saorsudp@telkom.net

Parsaoran Siahaan, et al.

preferred paired-molecule of this interaction becomes
the key factor to determine the solution structure. In
pairing-molecule, molecular polarity is important.
Polarity can affect interaction energy, geometry, and its
symmetry. Therefore, molecular geometry and
symmetry of paired-molecule can be determined from
13

1
C- H dipole-dipole reorientation of nuclear spin.
The different of melting point between benzene
and its derivative of hydrogenation had been explained
by different molecular orientation caused by different
symmetry [1] although this compounds group has
almost similar mass. Woessner [2] and Huntress [3]
studied the effect of anisotropy on nuclear spin
relaxation. Some of relaxation mechanisms were
reported [4,5] which included the study of hydrogen
bonding by NMR [6]. The amount of chemical system
which was studied by nuclear spin relaxation methods
was increasing [7-10], benzene and its derivative
included [8], and its theories also developed [11]. Some
of factors such as steric effect on flexible molecule
were studied [12], delocalised electron spin effect
through sigma bonding on relaxation [13] and hydrogen
bonding effect on anisotropic reorientation [14].

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Indo. J. Chem., 2007, 7 (3), 273-277

Although benzene liquid relaxation was studied, it was
reviewed by Dolle [15]. The relaxation study was
continued on simple system by synthesizing a
compound model, although it had been done on more
complex systems such as peptide [16].
Since molecular rotational dynamic sensitively is
affected by their chemical environment, therefore, in
order to obtain more accurately result of studies it is
selected the molecule which has the mobility not too
flexible and complex. For this purpose an appropriate
molecule is monosubstituted benzene compounds.
Phenylacetylene, Ph-CCH, which has a weakly acidic
hydrogen, theoretically it can interact through oxygen
with
hexamethylphosphoric
triamide
(HMPA),

OP[N(CH3)2]3. Based on these theoretically assuming
properties of interaction, phenylacetylene in HMPA will
show the anisotropic rotation motion, and it is interest to
investigate whether it is.
Is there interaction between Ph-CCH and HMPA
through acidic hydrogen of Ph-CCH with oxygen of
hexamethylphosphoric triamide (HMPA)? What is effect
of this interaction on rotational motion of Ph-CCH? PhCCH molecule has phenyl group which has similar
structure with benzene, it is rigid and low flexibility.
From the molecular shape, Ph-CCH is expected to
exhibit anisotropic rotational diffusion. HMPA molecule is
an exceptional solvent in that is has a quite large dipole
moment but comparatively low relative dielectricity
constant. Therefore, Ph-CCH molecule has a weakly
acidic hydrogen which can linearly interact with HMPA.
Then it is interest and important to investigate this kind
of interaction. Whether the interaction through acidic
hydrogen just only one possibility of configuration? In
order to know which are the configurations are preferred,
the Ph-CCH molecule in neat and in HMPA both will be

13
investigated by C NMR spectroscopy. The data of
relaxation time T1 will be determined and interpreted.
Based on the pattern of relaxation time T1 the
appropriate configurations of interaction between PhCCH and HMPA will be obtained.
In order to support the result of NMR
measurement, energy of interaction will calculated by ab
initio methods. Interaction energy will calculated by
formula ΔEk = EkAB – (EA + EB) [17]. The preferred
configurations of interaction between molecule Ph-CCH
and HMPA are determined based on the lowest energy
of each their paired-molecule. The objective is
investigation a deeper understanding of the behaviour of
rotational motion of phenylacetylene molecule in HMPA
13
solution through determination of T1 C spin-lattice time
relaxation.
EXPERIMENTAL SECTION
Materials
All materials are for NMR spectroscopy from

MERCK. Phenylacetylene (pa), Ph-CCH, (ρ=0.930;

Parsaoran Siahaan, et al.

purity 98%), hexamethyl-phosphoric triamide (HMPA),
OP[N(CH3)2]3 (ρ=1,030; purity 99%), solution 3%
phenylacetylene in HMPA.
Instrumentation
A set of distillation equipment, Mikro-KPGUbbelohde Viscometer and DMA 40 densitometer, a
set of glasses and vacuum pump equipment, NMR
Spectrometer of Bruker and
Jeol 500 MHz,
respectively, a set of software such as Gaussian 03
and Mathcad for calculation and analysis
were
used.
Procedure
13

Experiment of T1 C relaxation time by NMR

Neat phenylacetylene solution non-degassed
Dynamic viscosity, η=ρν, was obtained after to
measure kinematics viscocity, ν, at 303 K. NMR
spectrum was obtained by pulse methods at 302.5 K.
13
Relative intensity, Sn(τ), of each C nuclei peak with
variation of pulse delay time, τ, was measured by pulse
sequence π-τ-π/2 which is called inversion recovery
13
sequence method [17]. T1 C relaxation time each of
carbon atom was calculated from the intercept value
with τ axis graphic of Sn(τ) versus τ through Bloch
equation,



M z    M o 1  2e  T1



or

Sn    A  Be C ....(1)

Solution of phenylacetylene in HMPA nondegassed
It was done similarly to part (1) with in HMPA
solvent.
Calculation molecular geometry
Firstly, molecular structure model of single
molecule: Ph-CCH, HMPT, paired-molecule: PhCCH...Ph-CN, Ph-CCH...HMPT, with various
configurations were made. Matrix Z of each models
were constructed.
Then, calculating of molecular
geometry optimation was done by ab initio at theory
level RHF/6-31G(d). The result of calculation was
interpreted to confirm the T1.
RESULT AND DISCUSSION
13

Determination of T1 C relaxation time

Neat phenylacetylene solution non-degassed
The T1 time relaxation of carbon C1, C2,6, C3,5, C4,
C7 and C8 of neat phenylacetylene, Fig 3, was obtained
In other word, it was happened interaction between
phenylacetylene and HMPA molecule. Reduction was
higher than four times in C4 and C8. The reduction of
relaxation time was happened only if paired-molecule
between phenylacetylene molecule and HMPA was

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Indo. J. Chem., 2007, 7 (3), 273-277

(c)
H
13

(b)

H
C5

13

C6
(a)

H

C4
13

H

Fig 1. Curve of Sn versus τ for neat phenylacetylene

Fig 2. Curve of Sn
acetylene in HMPT

versus τ

for solution phenyl-

13

Table 1. T1 C Relaxation time of neat phenylacetylene
and solution in HMPT
13
T1 C/second
Carbon
Neat
In HMPT
C1
28,1817
6,6154
C2,6 (ortho)
9,8602
2,2281
C3,5 (meta)
9,8644
2,1764
C4 (para)
6,7179
1,0232
C7
18,5519
2,9354
C8
7,0550
1,0502
13

occurred. Therefore, T1 C relaxation time data by using
equation-1 as an exponential regression was given in
Fig 1. Data of T1 time relaxation listed in column 2 Table
1. Whereas the T1 time relaxation of carbon C1, C2,6,
C3,5, C4, C7 and C8 of phenylacetylene in HMPT, was
obtained by using equation-1 as an exponential
regression of Fig 2. Data of T1 time relaxation listed in
column 2 Table 1.
In neat phenylacetylene the carbon nuclear C1
13
and C7 have T1 C relaxation time longer than other
where there is no hydrogen directly bonded. Whereas
13
the similar T1 C relaxation time of orto and meta

Parsaoran Siahaan, et al.

13

13

C3

13

C1

13

C7

C8

H

C2
H

Fig 3. Three possibility of rotation axis of phenylacetylene molecule
Table 2. The ab intio calculation of single and pairedmolecule between phenylacetylene and HMPA
ΔEk/
Energy
Molecule
-1
kcal.mol
E/Hartree
Single:
1. pa
-306,3783
3
2. HMPA
-816,5731 192,255.10
paired:
pa…pa
-612,7577
-0,7530
pa…HMPT linear
-50,8041
pa…HMPT orto
1123,0323
-49,3167
pa…HMPT meta
-48,9407
pa…HMPT para
1123,0299
-48,9829
-47.2502
pa…HMPT
Interaction
Dipole
Molecule
distance
moment
o
r/A
µ/Debye
1. pa
2. HMPA

0,6893
1,9926

pa…pa
0,0004
3,1726
pa…HMPT linear
4,9521
(r3,15)
pa…HMPT ortho
4,2139
2,1408
pa…HMPT meta
2,4200
pa…HMPT para
6,0083
pa…HMPT
2,3863
layered
9,8602 and 9,8644 second, respectively, indicate the
13
similar C-H vector orientation with static magnet field
Bo. This happened if the Ph-CN molecule, Fig 3,
rotate in parallel axis (a) with -CCH substituen.
Solution phenylacetylene in HMPA non-degassed
13

The T1 C relaxation time of carbon atom C2,6,
C3,5, C4 was obtained included in column-3 Table 2.
13
The T1 C relaxation time in HMPA solution was highly
13
reduced. In HMPA solution the T1 C relaxation time of
carbon nuclear
C2,6 and C3,5, reduced average
approximately four times. Instead of their hydrogen
directly bonded, the reduced of relaxation time indicate
the lower mobility of phenylacetylene molecule.

276

Indo. J. Chem., 2007, 7 (3), 273-277

0A o
86

1,0
7

-0,2053 C
1,0
74

H39

C38

C33

H15

C32

C31

H30

O2

P1

H16
H18

N12
C17

C36

1,1882Ao

H37

C34

H19
H20

N21

H35

D(C2C1C5H6) = 0,0o

C22

C26

H29

o

A

H8

H11
H14

C8
N3

C42

119,4316o

0,2073

C4

120,3056o

74 3

120,3779o

0,2968

C3 1,0569Ao H4

-0,1830

1,0

2A o

71,3835Ao C5

119,7323o

-0,5475

0,1650

-0,0120

C1 1,4428AoC2

92 6
Ao

120,1905o

o

120,1100o

120,1577o

H7 H9 H10

C13

120,2912o

1,3

1 ,3

119,4031o

H5

H43
C40

119,4335o

o

o

61A

120,0501

120,1936

119,9009o

o

25A

-0,1930

1,0753Ao C9
8
1,3

H10

C13

9
1,3

C11

120,1542o

H41

-0,1828

1,3835Ao

o

-0,2054

0,2065

120,3730o

119,7332o

A
742

120,1127o

H14

43
Ao

1 ,0

H12

120,0490o

H6

0,2231

0,2073

H23
H24

H
H28 H27 25

(a)

H6

0,2230

H10

H9

(a)

H6

H43

H16
H18
H19

C17

N12

H20

P1
O2

C40

H23

N21

C22

H24
H25

H30
C26

C31

C38

H29

C32

C36
H37

H15

C13

N3

C41
H39

H11 H14

C8
C4

H5

C42

H7

H27

H28

H33

C34
H35

(b)
(b)
Fig 4. Molecular geometry of phenylacetylene (a)
values of parameters, (b) tree-dimensional structure.
1,0
8

o

1,0784 o
A

H7

116,8355o

1,6318

O2

P1

1,7113Ao

73
4A o
1,4

H10
H11

C8
N3

C39

-0,3070

H15

o

0,1823

0,1766

H30

C34

P1

C32

H16
H18

N12

H19
H20

N21

H19

H33

H35

H180,1766

C22

C26

H29

0,1823

H28

H23

H24
H27 H25

(c)

H20 0,1791
0,1766

H23

H25

O2

0,1823

34
Ao

H28

C31

C36

H14
H15

C17

H16

C17

-0,3070 C22

H27

H37

0,1791

N12

106,3463o

A
84
07
1,

0,1791

C26

1,08
43A o

o

0,1766

o

-0,3070
56A
1,07

C4

C13

H14

C13

106,3463o

-0,7600

N21 1,47

-0,7600

H29

C8 -0,3070

o

34A
N3 1,47 116,8335o
-0,3070

13A
1,71

1,4727Ao

112,4399o

H7 H9

0,1791

H11

109,9520o

1,711
3A o

112,4399o

-0,7383

C38

H10

o

-0,7600

H6
H5

H40

C41

0,1823

H9

4A
73
1,4

-0,3070 C4

C42

0,1766

43
Ao

6A
1,075

H5

0,1823

o

106,2460o

0,1766

H6

107,1534

0,1791

H43

H6

H24 0,1791

H38

0,1823

(a)

H40
C37

H7 H9 H10

H5
C4

H11

C8
N3

C39

C13
H43

C42

C41

C36

C31

H30

O2

P1

H14
H15

N12
C17

C34
H35

C32

N21

H33
H29

C26

suggested to forming Ph-CCH...HMPApaired-molecule.
From the molecular shape Ph-CCH is expected to
exhibit anisotropic rotational diffusion which in fact can
be deduced from the different set of T1 values. In HMPA
solution this set of T1 values of the ortho, meta and para
carbon nuclei was also exhibit anisotropic rotational
diffusion. It means the reorientation motion of
phenylacetylene is anisotropic. If this is happened the
paired-molecule seem lead to linearly shaped molecule.
From the view of molecular shape of phenylacetylene
and HMPA, which will also be calculated by ab initio,

Parsaoran Siahaan, et al.

H19
H20

H23
H24

H28

(b)
Fig 5. Molecular geometry of HMPT (a) values of
parameters, (b) tree-dimensional structure

C22

H16
H18

H27 H25

(d)
Fig 6. Molecular configuration of paired-molecule and
H-acidic
and
oxygen
distances
between
phenylacetylene and HMPT (a) linearly: r/Å=2.1408,
ortho: r/ which =2.4200, meta: r/ which = -, para:
o
r/A =2.3863.
this can only be happened for the linearly PhCCH...HMPA paired-molecule orientation.
Energy and geometry optimation of molecule
The result of calculation of energy and other
parameters are included in Table 2. Ph-CCH... HMPA
paired-molecule with linearly configuration had ΔEk
lower than others. So the linearly orientation, Fig 6(a),

Indo. J. Chem., 2007, 7 (3), 273-277

conform to the T1 relaxation time data of
phenylacetylene in HMPA. These results are also
confirm by the properties of single molecule, Fig 4(a).

5.

CONCLUSION
13

In the HMPT solution non-degassed, the C T1
relaxation time of phenylacetylene was reduced four
times.
It
means
spectroscopycally that
time
13
measurement of C NMR spectrum was also reduced.
In relation to the molecular mobility and its
interaction, similarly with in the neat, rotational diffusion
of phenylacetylene (pa) molecule in HMPA was
13
anisotropic. Similarity ratio of C T1 relaxation time C2,6
and C3,5 with C4 and C8 in HMPT explains that the
linearly interaction through H-acidic of HMPT and
oxygen in HMPT was occurred.
Linearly
shaped
paired-molecule
structure
pa…HMPA was preferred than others shaped of pairedmolecule configurations. This fact also confirmed by ab
initio calculation.

6.

7.
8.
9.

ACKNOWLEDGEMENT
10.

This work was supported by the BPPS, DAADsupported Partnership TUB-ITB-UNDIP in Chemistry
2003-2006
scholarship.
Hopefully,
I
gratefully
acknowledge support for DAAD, Prof. Dieter Ziessow
from Stranski Laboratory for Physical and Theoretical
Chemistry, Institute of Chemistry, Technical University of
Berlin, and Indonesia Government.

13.

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14.

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with

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