Charge transfer and ups study of substituted thiophenes

35

Joumal of Molecular Structure. 114 (1984) 35-40 Ekevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

CHARGBTRANSFER L.

AND

Nyul&szi,

Dept.

of

1521-H.

T.

UPS

STUDY

VeszprAmi,

Inorganic

OF

73. Zimonyi

Chemistry,

Budapest,

SUBSTITUTBD and

Technical

THIOPHBNES J.

Xagy

Univ.

7

of

Buaapest.

Hungary

ABSTRACT Linear correlations between the first Tao ionization potentials and CT band energies for substituted thioptenes have been obtained. The substituent effect has been systemaiiceily discussed and i:?terpreted by the consideration of the symmetry of the molecular orbitals.

INTRODUCTION In

our

previous

propeLTties

of

atom.

By

the

first

UV

band

of

some

works

help

(refs.l.2)

five-membered

some

of

the

vibronic

thiophene

of

heterocycles

has

have

been

investigated

vie

heterocycies assigned.

considered

spectral one

t h e s;jmmetry

structure

been

the

ccntaining The

using

of

orbital

hetercthe

ordering

quantum-chemical

calculations. The

aim

tituent

the

of

purpose

lexes nes

this

effect

tation_ this

of

as

have

on

work

is

thiophene

interaction the

a systematic

charge the

ring

transfer

ionization

well

as

been

studied.

and

between

investigation the

of

spectroscopic

the

ring

and

(CT)

band

energies

potentials

of

the

i.he subs-

inter_pre-

substituent.For of

TCMB

substituted

camp-

thiophe-

EXPERIMENTAL Complexes

were

investigations thiophenes UPS racy UV

were

spectra

of

the

spectra

0022-2860/84/SO3.00

formed

halogen,

by

synthesized were

measured

measurement were

was

recorded

0 1984

O.im

TCNE

solution

trimethylsilil-

Ekevier

by

the

using

(TXS)

usual

in and

CFi2Ci2.

For

methods.

pie-1 resonance

line.

The

zcc:l-

0.05eV. on

SPECORD

Science

Publishers

the

ter-t.b:_:tyl-(t.Bo)

iJV VIS

B.V.

sgactrophotoneter.

:..

,.

.J(j

,.

:

RE'SULTS Since

the

resonance

.band'.maximum depends

on

obtain-

two

linear owing

the

of

different

equ ations

for

the

the

two

analyses

coefficient the 'first

maxima

as

in .Table

order

to

and

In

th_e case

The

effect

of

indication

of

reasonable

highest

the

error

and

IP-s.

used.

are

O.lleV

calculated

thiophene

substituent

first

and

the

releasing

f0r.tk.e have be

first a,(n)

used

mesomerio

for

effect

effects

groups groups and and

is

IP.

IP-s

I?

the

opposite.

I?.

are

the

The

in

increase. This

first

two

(Further

derivatives.)

suhstituent

92

first two IP-s -1, -M effect.

the

compounds.

values

symmetry.

substituted of

of

is

n

feet.&&

H

H

inn smaller

H

tk

.; : : f!

SW

of

0.864

consider

the

second b,(x)

we

orbitals

aa

The

the -foll-

observed

a6

the- case

the

second

a4

,Fig.l.

to

For

respectively

for and

ii40 occupied

withdrawing

electron

the

the

0.982

as

the the

electron

k-ill also

su'sstitution

CT

1.

different of

and

and

well

evaluate

shift of

the

potential

it was

was

(2)

summarized

between

ionization

(ref.3)

(1)

Th_e CT. band

orbitals

and

orbital

iP2=~.33E2t5.11

for

is

complex

relationship

k-ere obtained:

regression

effect

the

IP,=l.58E;'4.52

and.0.15e'l

In

in

a l-east square

correlation

position

TCNE

the..questiqnable

equa'tions

The

factor

,-*I

-’

The first two IP-s Fig.2. the case of. +I, +M effect.

in

this

37

a 0 CvuJmcOOOT-7

.

00000

.

.

0

--naJm

.

.

v--m . . 000

.

cr.ir\oG-rnc-4 oo\lmomm

.

.

000000

.

.

.

.

7-*r-T-

c-. co

?TT

00

.

000

.

.

.

0000

0’

mYj

mo . . .

.

_ :,

:

_3’8.‘.

I

..

..

‘_..

.’

.,

for the b.than fpr the a2 orbital, because the former one is .. and on the a carbon atoms. mSinl.$ localised on the heteroatcm In o,%der,to.neasu_re the- splitting of the IP-s relative to thiophene

a ,ii.value is introduced

for-the

i-th

substituted

'thiophene .as follows A;=

( IP2 - I'&-

A i is negative creases..

( IP2 - IP

as the. splitting

1 jthiophene

decreases,

and positive

as in-

In the case of .thiophene, Q- and p-bromo-thiophene the error of. the UPS measurements is.O.001 eV (ref.6). for the other compounds

0'.05 eV

Therefore

(ref.7,8).

the error

of Ai is 0.07

eV

for most of the compounds. For the Q- and p-bromo-thiophene it is 0.02 eV; and in the calculated IF-s (marked with letter c in Tab.1). the error is 0.2 eV. First we consider the investigated substi_tuent effects in ~1 position in sequence and try to assess to their relative magnitude values. -1, -M effect Due

( -COOMe.

-COOH.-CHO.

-NO2

arouos,

on bl orbital

to the shieldingeffect

Fig.

1 )

the -M effect

is stron-

ger On "2 orbital and it is stabilized more, than the bl. There"$0. ( It should fore the splitting of the orbitals decreases, be noted,

that

AC002.1eand

+OOH

+I, ill effect

( -Me,

-t-au

The +M effect

is the result

are less

srouos,

Fig.

than

the error

2

of the hyperconjugation

bl level rises less than the a2. Thus the splitting A?O. On 2,5-dimethyl-thiophene this effect is more -I. +M.effect In this

case

( halogens, the splitting

-SMe

srouo

of Ai)

Fig.

of the orbitals

and

the

increases, considerable.

3 ) increases,ni>O.

The

reasons are similar, than in the,case of +I, tM effect. From the Cl to I the. -1 effect decreases ( when the electronegativities are taken into account a +I effect is expectable in case of iodine), the +M effect increases. ( .The stabilization of the

39 orbitals

a

aH

a2 84 06 88%

the

decreases,

disubstituted

Br

-

I

-’

increases.)

The

splitting

in

the

ir.ore significant.

X=

H

H

H

ms

H

*

7 :

:

--..’

is

pb

1

1

1

splitting

corrpounds

:

-

92 bl

94

-.

h -.

‘. -

*-*

-_.-

96

the

The first two IP-s case of -1. tM effect.

+I,

-M

Fig.3.

it

effect is

difficillt

The

grcup.

this

resultant tal

(-M)

(-TMS,

of

en

effects

electron

group as

this

a result

sey

effect

is

effect

the

derivatives

(ref.10). substituent the

of

TNS

the

and

corrpour-ds

SiH3

groups

hyperconjugative

b1

orbitals can

smaller.

rzentioned

on

(+I)

destabilized

releasFng of

the

Fig.4.)

any

of

i!l

belozlg

is

(+!*I)and

to

the ci-orbi-

(ref.10). the

is

As

wether

inductive

conjugation

effect

groups,

corr,plex effect

the

Considering

-SiH3 to

t1.:0 I?-s The i'irst Fig-L. the case of +I,-!1 effect.

in

more

is

orbital

The

significant

be

splitting

be

stronger

in

p position the

in gets

d-orbital

to

and

cozparel

expected.

shift

in

the

of The

analogous

is

no

SiH7 prosurzab 1 y

szaller

effect.

the

there of

rjith thiophene case

hype _rbenzene

shielding

orbitals

is

. 40

the ‘same,.-and

almost

only

exception

ficant be

is

decreasing

the

the in

~~~ -values

are

nearby

the

P-trimethylsilylthiophene, the

splitting

of

the

error. where

orbital

The 2

signi-

energies

can

observed.

ACKNOWLEDGEMENT One

( the

of

us

( T.

University

spectra,

and

for

V.

) is

of

Tokyo

their

most

grateful

) for

their

hospitality

and

to Y. help

to

Haralia measure

and

K.

the

Ohno UPS

friendship.

RZFERENJES

117

97

(1983)

S. Santini, G. Savelli, J. Chem. Sot. Faradn:y I 4 G.G. Aloisi, 71 2045 (1975) 5 KA. Pudoba, E.A. Pukevic, Izv. Akad. Nauk. Latv. SSR Ser. Khim. 259 (1982) 6 J.W. Rabalais, L. Karlsson, K. Siegbahn, L.O. Q?erme. T. Bergmark, int. J. Mass.. Spectrom. ion Phys.,z 185 (1972) G. Flarino, A. Taticchi, G. Distefano, F.P. 7 F. Fringuelli, Colonna, S. Pignatoro, J. Chem. Sot. Perkin II 276 (1976) 8 A.D, Baker, D. Betteridge, N.R. Kemp, R.E. Kirby, Anal. Chem. 42 1064 (1970) 9 K Modelli, G. Distefano, D. Jones, J. Seconi, J. Electron 31 63 (1983) Spectr. Rel. Phenom. J. NagyrJ. Organomet. Chem. in press 10 T. Veszpremi,