UPS investigation of 1-substituted pyrroles

JournalofMo~cularStructure,218

Elsevier

Science

Publishers

UPS Ii~VESTIGATIGil OF L.

PIYULASZI, T.

and T.

201

(1990) 201-205

B.V., Amsterdam

-

Printed

l-SUBSTITUTED

in The Netherlands

PYRROLES

TUTH, GY. ZSLMBOK, G. CSOIIKA, J.

RiFFY,

J.

NAGY

VESZPREMI

Department of Inorganic Chemistry H-1521 Budapest, Hungary

, Technical

University

Budapest

SUI;IIsIARY He I UPS spectra of l-substituted pyrroles has been investigated and interpreted using MNDO quantum-chemical calculations. The substituent effect of alkyl and silyl group on the pyrrole ring has been discussed. INTRUOUCTI011 The substituent rings has of

(benzene been

effect (ref.

of

11,

investigated

the

furane

trimethylsilyl (ref.

2)

by photoelectron

group

on aromatic

and thiophene

spectroscopy

(ref. in

3))

a series

papers. Since

attached might

in

the

case

to

the

heteroatom

be somewhat

In the

of

l-substituted of

pyrroles

the

aromatic

paper

pyrrole,

1-methyl-pyrrole,

2,5-dimethyl-pyrrole, and

by He I photoelectron

been

investigated

and quantum-chemical

assignment the

was investigated

(refs.

4-6)

and proving

n-levels

l-

1-trimethylsilyl-2,5-dimethylspectroscopy

calculations.

itself

spectroscopy

is

l-trimethyl-

tert-butyl-2,5-dimethyl-pyrrole

Pyrrole

group

interaction

1,2,5-trimethyl-pyrrole,

-pyrrole

have

silyl

the

modified.

present

silyl-pyrrole,

the

ring,

(refs.

thoroughly

providing the

a clear

applicability

by photoelectron picture

of

of

Koopman’s

the

band

theorem

for

7-B).

EXPERIMEIITAL The compounds (refs.

9-101,

investigated

their

purity

The photoelectron Spectra 2P 2,3

were line rtith

was checked

spectrometer

recorded

at

synthesized

the

by known methods

by gas

chromatography.

was described

He I resonance

earlier line,

(ref.

FWHMat

11). the

was 45 meV.

Quantum chemical method

were

complete

0022-2860/90/$03.50

calculations geometry

0 1990 Elsevier

were

carried

optimization

Science

Publishers

out (ref.

B.V.

by the 12).

MN00

Ar

202

RESULTS,

1,

OISCUSSIOlJ

The

UPS

and

Fig.

spectra

2,

summarized

in

1.

The

other

He

first

most

two

rent

molecule.

n

well.

broad

band

ristic

of to

three

centered trimethylsilyl orbitals

of

at

in

Using

as

compoullcis calculated

arc

orbital

shown in

Fig.

erlergirs

art:

8 IE/eV

l-substituted

low

the

In at

could the

are the

calculations

Koopman’s

peaks

pyrroles

energies while

spectrum,

levels

two

anti

IO

bands

each

these

orbitals,

ted

12

two in

invest.iyated

I.

I UPS spectra

peaks

vatives

the

positions

Table

14

16

Fis.

of

peak

case

as

theorem be

10.6-10.9

eV appears. mainly

for

from the

case

of

a2

the

This l-3)

2bl

at

silicon

band and and

paderi-

and

derivatives

(refs.

the

upper-

substituted

the

trimethylsilyl

derivatives localized

the

the to

separated

holds

in

for

related

of

well

same

is can

a charactebe

carbon

relaatoms,

203

14

16

2.

Fiy.

spectra

UPS

pyrrole. in

12

ayreement

with

appearance

of of

The splitting mesomeric perties plane

effect of

through

should the

dimethyl of

the

ained.

results the

the

first

substituent

two

corresponding

of

of

A

negative

the

at the

investigated if

due

by the

respectively,)

bands

11.5

the

the

is

difficult

characteristic the

substituent.

to

has

than

atom.

If

the

(pyrrole

substracted

from

a new value first

pro-

a nodal

orbital those

compounds

the

nodal

This

substituent

the

of

different

The a2 orbital

of

due

bands.

is

molecule splitting

2,5-dimethyl

to

nitrogen

parent

eV is

overlapping

bands

and the

affected largely

of

of

calculations.

orbitals.

heteroatom

pyrrole, is

number

the

two bands

MN00

belob

bands

of the

derivatives

of

of

localized first

8 IE/eV

l-substituted

a great

be much less

synxletry, of

the

of

the

The assignment the

lo

of

bl

splitting and 2,5-

the (A)

bands

splitting is

obt-

decreases

204

TABLE 1 Ionization tigated

energies pyrrole

pyrrole

l-methyl-pyrrol.e

MN00

IE

and HNDO orbital

energies

(eV>

for

the

inves-

derivatives

l-tert-butyl-pyrrole

IE

FIND0

l-trimethylsilyl-pyrrole

MN00

IE

MNOU

a.22

a.56

1.95

a.55

8.46

7.9

8.30

9.22

9.33

8.80

9.23

9.15

fi.80

9.05 11.55

10.9

11.63 11.63

12.7

13.10

13.07

12.51.

13.50

11.9

13.32

12.91

13.17

13.85

12.87

12.3&l

13.66

12.4

12.87

2,5-dimethyl-pyrrole

1,2,5_trimethyl-pyrrole

2,5-dimethyl-l-tert-butyl-pyrrole

IE

IE

MN00

IE

MNDO

IE

FIND0

MN00

2,5-dimethyl-ltrimethylsilyl-pyrrol.e

7.49

8.43

7.23

0.42

7.22

8.31

7.34

6.20

8.78

9.36

8.35

9.26

8.30

9.22

8.53

Y.13 11.51

10.6

11.55 12.23

.2.1

12.81

which the of

11.1

10.9

12.67

12.86

13.07

12.45

1.2.96

13.00

12.51

12.10

13.01

that

the

corresponding

effect

of

the

substituent

the

12.0

13.10

means

+M

12.30

For

a2 orbital.

bl in

substituents

orbital

energy

is

greater

extent

than

having

-M effect

A

are

and

raised the

by

energy

should

be

positive. In the for

the

tives, -pyrrole

case

of

l-methyl

corresponding respectively. A

is

-0.21

substitution

pyrrole In the in

A

and the case

agreement

of

-0.15

‘2,5-dimethyl

pyrrole

-0.17 deriva-

l-tert-butyl-2,5-dimethyl-

with

the

somewhat

larger

hyper-

205

conjugative be

effect

mentioned,

five

membered

but

this

In

the

cf

ring

distortion case

of

the

tert-butyi

, that

horrevcr is

somewhat

has silyl

group

according

to

puckered

only

slight

(ref.

due

effect

substitution

is

A

13).

(It

should

MN00 calculations to on -0.1

the

the

steric

strain

n orbital

energies.)

indicating

a small

+I:<

effect. If

data

membered groups the

are rings

a larger latter

rious

aromatic while

observed, concluded. on

one

the

This substituted

compared

to 2,

(refs.

+M effect the

effect

rings. fcr

those

3)

In

obtained can

be

is

observed

is

small,

the

furane

change

it

might

case and

previously

concluded than

and of

for

possibly

silyl

changes

thiophene

pyrrole

that

small to

be

fcr

other

fcr

alkyl

groups.

sliyhtly small

For

for

va-

-M effect

+M effect related

five

could to

the

was be

charge

atom.

REFERENCES 1 2 3 4 5 6 7 e 9 10

:: 13

T. VeszprBmi, 115 T. Veszpr&ni,

Y. Harada,

K. Ohno, H. M&oh,

J.

Organomet.

Chem., 244

Y. Harada,

K. Ohno, H. Mutoh,

J.

Organomet.

Chem.,

(1X3)

2 52 ( 19 83)

121 T. VeszprBrni,

L. Nyulaszi, J. Nagy, 3. Organomct. Chem. -.331 (1987) 175 T. Clunakata, K. Kuchitsu, Y. Harada, J. El. Spectt. 20 (1980) 235 J. A. Sell, A. Kuppermann. Chem. Phys. Lett. a(197v355 L. Klasinc, A. Sabljic, G. Kluge, J. Rieger, M. Scholz, 3. Chem. Sot. Perkin II (1902) 539 M. H. Palmer, A. J. Beveridge, Chem. Phys. UC19871 24Y bd. von iliessen, L. 5. Cederbaum, G. H. F. Diercksen, J. Am. Chem. Sot. 2a (1976) 311 H. Heaney, S. V. Ley, J.

Chem. Sot. Perkin I (1973) 499 H, S. Broadbent, W. S. Burnham, R. K. Olsen, R. M. Sheeley, J. :hem. 5 (1963) 757 T. VeszprBmi, Gy. Zsombok, Magy. Kern. Foly. 92 (1986) 39 i/i. 3. S. Oewar, W. 3. Thiel, J. Am. Chem. Soc.99 (1977) 4897 T. VeszprBmi, J. Nagy, J. Organomet. Chem. 225m83) 41

Heterocycl.