Nuclear quadrupole coupling in the microwave spectrum of 1,2,3-triazole

JO,~K~AI. OF

MOLE(‘I-LAR

Nuclear

65, 313 318 ilc)iii

S"E(‘TROSCOPY

Quadrupole

Coupling in the Microwave of 1,2,3-Triazole

Spectrum

The hyperfine structure in the microwave spectra of 1.2,Striazole and .V-deutero 1,2.3triazole has been analyzed. The coupling constants derived from the analysis of each isotopic species have heen combined to give the principal nuclear quadrupole coupling constants at the sites of the three inequivalent 14K nuclei. INTRODUCTION

In a recent first

time

paper

the

on the microwave

analysis

containing

three

quadrupole

coupling

of the

inequivalent

C’, symmetry

an equilibrium should

hyperhne

nuclei.

in the isomeric are possible

1Ve have

molecule

for 1,2$triazole.

between

these

tautomers

for the

in a molecule

now measured

1,2,3-triazole

and the 2-H form of C‘?,, symmetry.

established

(I) we reported structure

the nuclear

and we report

These

are the

In the gas phase

and the microwave

the

1-H form

there

spectra

will be of both

be detectable.

The

spectrum

of the

1-H tautomer

symmetrical

2-H tautomer

cerned

the l-H,

with

The

measurement

molecule

allows

molecular esting

of 1,2,4triazole

quadrupole

quadrupolar

constants

results in this paper. Two tautomeric structures having

spectrum

nuclear

and the 1-deutero of quadrupole

the determination

principal

principal

inertial

has been

has onlv recently

known

isotopic coupling

forms

axes and hence

constants

coupling

field gradient

EXPERI~JESTAI,

time

(1) while

(3j. Our analysis

the

was con-

of 1,2,3-triazole.

of the off-diagonal

axes of the electric

for some

been observed

in two tensor

constants

tensors

isotopic

elements

species relative

of a to the

in the chemically

inter-

(4).

DETAILS

1,2,3-triazole was synthesized by the method of Wiley et al. (5) and purified by fractional distillation and gas chromatography. The purity of the sample dissolved in CDC18 was checked with

by NMR

(6). S-Deutero

triazole

was made

by direct

exchange

DsO.

The Stark

modulated

microwave

spectrometer

employed

an absorption

cell consisting

of a 3.5 m length of G-band waveguide (2.215 X 4.755 cm2), the large size of which improved resolution by reducing broadening due to wall collisions. All spectra were

1Present address: Victorian College of Pharmacy, Royal Parade, Parkville, Victoria. Australia

C‘opyright .X1 rights

@ Ir)ii

by

of reproduction

.4cademic in any

Prese, form

Inc. reserved.

314 Table

Nuclear

S’uadrupole

Coupling

1

I

Constants

for

,2,3-trmzo1e

1,2,3-triazole

(MHz)

N-Deuterotrmzole

xGa

(‘1

0.64~0.2’8”

0.55+0.16

Yhh

0)

3.22

3.32

x

0)

-3.86

(1)

-1.04

cc

Xab

x ah x

aa

Xbb x

Xab

(3)

* E.-:O:S

-1.37+0.13

2.57~0.14

(3)

ectmnted

-0.82

2.19

2.19

0.90

3.76

from the

+_ 0.43

-3.33

-4.7750.14

C3’

5 0.12

0.53

1.17

(”

t3’

-2.58

0.53

t2)

cc

0.91 2.04

-4.15t0.17

Xbb (2)

50.88

-3.86

3.62~0.14

)
x cc

5 0.44

fit of the contour

i

0.41

maxima

recorded using a Varian X-12 klystron source that was phase locked via a Microwave Systems PL 5 microwave oscillator synchronizer to a 50 MHz VFO harmonic produced in a Micronow Model 1OlD frequency multiplier chain. The microwave frequency was scanned by sweeping the 50 MHz VFO signal and was measured by a Hewlett-Packard 5243/562A frequency counter. Stark modulation was provided by a 3 kV 10 kHz solid-state square-wave generator. All measurements were performed at 20°C with a sample pressure -2 Pa. Typical FWHM of 40 kHz was achieved for fully resolved components. ANALYSIS

01’ THE

SPECTRURI

The presence of three inequivalent 14h’ nuclei in 1,2,3-triazole causes the molecular rotational energy levels to be split into a set of hyperiine levels. Consequently transitions between rotational states are split into a number of components. The theory presented in an earlier paper (7) allows for the calculation of frequencies and relative intensities of transitions as a function of the quadrupole coupling. Convolution with a Lorentzian line shape function then gives rise to a contour representing the perturbed rotational transition. If the hyperfine transitions contributing to the contour are fully resolved then each peak in the contour can be associated with a specific hyperfine transition and it is

I-

-3-O

-4.0

-2 0

H

C2.3

-TRIAZOLt

20

1.0

-1.0

4.0

3.0

mtir

VO

1’1(:.

1. Otxrrved

then

computer-simulated

and

possible

to use a least-squares

from the frequency

differences

As the number for example

of hyperfine

when

the resolution

the number

is poor,

in the contour of the

multiplets for the

then

to specific

hyperline

procedure

between transitions

it becomes

structure

in the

20:!

transition of 1-H 1,2,.3-triazolc;

to determine

the hypertine within

of quadrupolar

hypertine

21, +

a rotational

nuclei

difficult

lines

transition

of 1,2,3-triaaole.

are

adjusted

not

fully

resolved,

the coupling

the convoluted

spectra

constants

we implemented until

a least-squares

differences

were well represented. 1-D

between

The coupling

(as

(I, 7)) or if

individual

occurred

peaks

in the analysis

For example,

&r + Jr,! transition is composed of over 300 hyperfine components. In order to overcome the difficulty of extracting the coupling constants that

constants

increases

increases

to assign

This situation

rotational

coupling (8).

in a molecule

or impossible

transitions.

the

transitions

fitting

maxima

from spectra procedure

that

in the contours

constants

obtained

1,2,3-TRIAZOLE

I;I(:. 2. Ohservcd and computer-simulated

= 13932.14

multiplets

MHz

for loi +

0~ transition

of 1-I)

of

by this

‘01 c--o0 $0

the

1.2..3-triazolc.

316 Tdble

Rotational

Constants

2

and Angle

of Rotation

1 , 2 ,3-triazole

of Prmcipal

Axes

N-Deuterotrmzole

A (GHZ)

IO.03071

9.96773

B (GHZ)

3.87056

9.16017

c

4.97296

1.77178

”

(GHZ)

36^

o”

method for both isotopic species of 1,2&triazole are listed in Table 1. Typical agreement between spectra calculated using these coupling constants and observed multiplets is shown in Figs. 1 and 2. The detailed analysis of the hyperfine structure leads to improved center frequencies for the rotational transitions and hence to more accurate rotational constants. The rotational constants for both isotopic species of 1,2,3-triazole are given in Table 2. DISCUSSION

The quadrupole coupling tensors for each isotopic species are related by a known rotation of axes in the molecular plane (CI = 36”, Fig. 3) and the off-diagonal tensor elements for each nucleus may be derived by rotating the tensor of the deutero species into the parent isotopic species. The values so obtained are given in Table 1. Diagonalization of the resulting complete tensors give the coupling constants expressed in the

‘I

H (4)

Flc. 3. Approximate orientation

of inertial axes for 1,2$triazole.

Table

3

N(1)

0.27

3.56

-j.afi*

0.858

N(2)

0.53*

3.79

-4.33

0. 752

N (3)

2.19

2.6H

--I.87

O.liJl

.m, =

*

angle

of orientation

to inertial rotation

*

of principal

axes.

i

of axes

with

uut-of-plane

xcc

quadrlpole

1.5 pose,ve

19.4”

R.-i0

-6.5”

axes

relative

for an are-c10ckw1se

molecule

oriented

as

,n Tlg.

3.

values.

TABLE 4

Some

Principal

Quadrupole

Coupling

Constants

Pyrazole

Imidazole

-3.018

-2.537

for Other

1

,2,4-triazole

-2.35

0.177

v

(a)

0.536

CL

(P,)

0.794

0.60

I

iBl)

0.647

0.720

i\ I (Ii21 TI

0,)

Molecules

(NI)

2.21

0.120

0.102

II and

B refer

envuonments

*

I

to

13

N nuclei

I* “pyrrole”

respect1ve1y.

is the out-of-p1

ane

coupling

constant.

and

(Nl)

0.858

0.53

(Nz:

(NP)

0.752

(N4)

2.19 0.101

._ *

,2,3-triazole -3.86

0.553

2.258

1

“pyndn”

-type

(N3)

principal

axes of the electric

quadrupole

coupling

Following

the arguments

nuclei

for

shown

in Table

1,2,+triazole

pyrrole-type

field gradient

constants

used in assigning (I)

and

nucleus.

nucleus

Table

(9) the coupling

3 lists the principal

in 1,2,3_triazole.

the quadrupole

imidazole

4. The large out-of-plane

nitrogen

at each

for each nitrogen

coupling

assignments

constant

data

for

for S(1)

to specific

1,2,3-triazole

are

is characteristic

of

environments.

Some

INDO

(10)

deviated

even

further

calculations from

were

the

done

for

experimental

1,2,4-

and

observations

1,2,3-triazole than

but

those

these

reported

for

of 1,2,3-triazole

the

imidazole. It is interesting out-of-plane (XL =

-

pyrrolic such

to observe

coupling 2.70 MHz

nitrogen

systems

value

prevailing

stant

as compared

electrons

with

density

azoles

and 1,2,4triazole,

at

the pyrrolic

In contrast,

pyrrole,

that,

implying

shows

perhaps

rather

than with

Table

nitrogen

imidazole

in the case of XX in triazole,

by the direction

away

from

as was found

that

of pyrrole

N adjacent

to the

1) implying

is enhanced

a diminished greater

N, lone pair,

bisector

of the ring angle,

in the case of pyrazole indicate

but we cannot

of 1,2,3-triazole

that

pursue

is established

December

the direction

of the 2 axis of the field gradient

the external

the Z axis for A-;$would

RECEIVED:

nitrogen

in magnitude

that above

for the

coupling

con-

delocalization

of r

in imidazole.

as evidenced bond,

is greater

for pyrazole

n-electron in pyrrole.

We anticipate deflected

for the pyrrole-type

X,(a),

(11)). This is also the case for other

(see values

the

that

constant,

(4). We might

of the c lone pair orbital, tensor, towards

expect

will be somewhat the adjacent

that

the lone pair is somewhat

detlected

this interesting

until

and the directions

situation

of inertial

N-H

the direction

of

away from the

the ring geometry

asis are likewise

located.

20, 1076 REFERENCES

1. G. L. BLACRMAN,

I<. L). E&own-,

2. 0. L. STIEFVATER,

Y.

R. BURDEX, AKU 4. ~MISHRA,

J. Mol. Speclvosc.

57, 294 (1975).

H. JONES, AND J. SHERIDAN, S’pectuoclri~~z..4&z A 26, 825 (1970).

3. N. NYCAARD ef al., prixate

communication,

February

1976.

zl. G. L. BLACKLI.\K, R. D. BRO\VK, I;. R. BURDEN, AND A. MISHRA, J. 1Mol. Sfr~tcttrre 9, 465 (1971). 5. R. H. WILEY, K. F. Hussvh-c, 6. T. J. B,~TTI
AXD J. MOIWA’I’, J. Org. C/ler,t. 21, 190 (1956).

Al. R. of Simple Heterocycles,”

Vol. 2. p. 219, Wiley,

New York,

1973.

K. ROI,TOS. R. I>. BROWN, I;. R. BVRDICK, AND A. MISHRA, .r. ,Wol. Spectrosc.

47, 457 (1973). 8. G. I,. B~,\csa~.\x. R. I). Bno\~r,

SAND1;. Ii. BURDES, J. Moi. .Speclrosc. 36, 528 (1971).

9. G. I,. B~..\cwnr,\s. R. I). BIK~w~-, F. R. BITRDI’.S, .XND I. R. ELS~QI, J. Mol. Spectrosc. 10. J. A.

P0l’I.K

New York, 11. 6.

AND I).

L. BE\.ERIDGlS, “.%pprosimate

Afolecular

1970.

BOLTOX AND R. 1). GROWN, .ltrsf. J. P/r_vs.27. 143 (1974).

Orbital

Theory,”

60, 63 (1976). McGraw-Hill,