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ESR of Gamma Irradiation andUltraviolet Photolysis Productsin Some TetrasubstitutedAmmonium CompoundsFevzi Köksal a , Recep Tapramaz a & Mehmet DuranDülkar aa Physics Department, Faculty of Arts and Sciences ,Ondokuz Mayis University , Samsun, TurkiyePublished online: 23 Sep 2006.

To cite this article: Fevzi Köksal , Recep Tapramaz & Mehmet Duran Dülkar (1992)ESR of Gamma Irradiation and Ultraviolet Photolysis Products in Some TetrasubstitutedAmmonium Compounds, Spectroscopy Letters: An International Journal for RapidCommunication, 25:3, 317-325, DOI: 10.1080/00387019208018190

To link to this article: http://dx.doi.org/10.1080/00387019208018190

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ESR OF GAMMA IRRADIATION AND ULTRAVIOLPT PHOTOLYSIS PRODUCE IN SOME llnRAsmTITurED AMMONIUMCOMPOUNDS

Key words: ESR, ultraviolet, photolysis, tetrasubstituted

Fevzi K o k s a l , Recep Tapramaz and Hehret ~ Z U I Diilkar Physics Department, Faculty of Arts and Sciences,

Ondokuz Mayis University, Samsun, Turkiye

The electron spin resonance of gamma and ultraviolet irradiated tetrabutylammonium halides [CH3(CH2)3] 4NX (X=I,Cl,Br) , tetrabutylammonium hydrogen sulfate [ CH3(CH2)3]4NHS04, tetrabutyl- ammonium periodate [CH3(CH2)3] 4N104, and ultraviolet photolyzed tetramethylammonium iodide, (CH3)4NI, and tetramethylphosphonium iodide, (CH3)4PI have been investigated between 140 and 350 K. The gamma and ultraviolet irradiation damage centers in tetrabutylammonium compounds were attributed to CH3-CH"CH'ZCH2, radicals, and ultraviolet photolysis damage centers in tetramethyl- ammonium and phosphonium iodides were attributed to CH3 radicals. The g values of both radicals are found to be isotropic and g = 2.0030 and 2.0037 respectively to the methylallyl and the methyl radicals. The hyperfine coupling constants of the free electron to the protons in the radicals are reported and discussed.

317

Copyright 0 1992 by Marcel Dekker, Inc.

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318 KOKSAL, TAPRAMAZ, AND DULKAR

INTRODUCHON

Irradiation of solids by y and X rays and ultraviolet light is well known to produce trapped radicals and electron spin resonance (ESR) investigation provide the most complete infor- mation. With ESR technique it has been shown that the photolysis and gamma irradiation of olefins produce allylic radicals at low temperatures [ 1-41. Allyltype of free radicals have been observed also at room temperature in gamma irradiated butene, butadiene, carboxylic acids and derivatives [ 5 1 and in X-irradiated glutaconic acid 1 6 1 . Methyl radicals have been observed by many authors [7-10]. As a continuation of our work on tetrasubstituted ammonium compounds 1111 we have investigated the gamma irradiation and the ultraviolet photolysis products in tetrabutylammonium halides [CH3(CH2)3] 4NX (X=I,Cl,Br), tetrabutylammonium hydrogen sulfate [CH3( CH2) ] 4NHS04, tet rabut ylammonium per iodate [ CH3( CH2) ] 4N104, tetramethylammonium iodide, ( CH3)4NI and tetramethylphosphonium iodide, (CH3)4PI. We have attributed both the gamma and ultraviolet irradiation products to methylallyl radicals in tetrabutylammonium compounds, and ultraviolet photolysis products to methyl radicals in tetramethylammonium iodide and tetramethylphosponium iodide.

The compounds used in this study were obtained commercially in powder form. The tetrabutylammonium iodide single crystals were grown in the laboratory from concetrated isoamylalcohol solutions. The single crystal parameters for tetrabutylammonium iodide were kindly obtained for us at the Hacettepe University in Ankara by X-ray -diffraction technique. The crystals are tetragonal with unit cell dimensions a = 10.32 8, c = 37.25 2 and 2 = 8. We could not grow the single in spite of our several attempts. The other tetrabutylammonium single crystals were grown in their concentrated aqueous solutions, but their single crystal

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TETRASUBSTITUTED AMMONIUM COMPOUNDS 319

sc

FIG.l. Crystal habit and the axes of tetrabutylammonium iodide single crystal.

spectra are the same of tetrabutylammonium iodide and their crystal structure data do not appear in literature.

The single crystals and powders were irradiated at room temperature by a 6oCo gamma ray source of 0.3 Mrad h-l for 5 h. The ultraviolet photolysis were made directly in the ESR cavity by a Conrad Hannovia 1 kW xenon lamp. The ESR spectra were recorded with a Varian Model 6109C ESR spectrometer using 10 mW microwave power and 100 kHz modulation. The low temperature measurements were carried out using a Varian variable temperature control unit. The g factors were found by comparison with a DPPH sample (g = 2.0036).

RBsDtTs AND DISCUSSION

The ESR spectra of gamma irradiated tetrabutylammonium iodide single crystal and powder samples exhibit a septet with an approximate intensity distribution of 1:6:15:20:15:6:1 and a spacing of 14 gauss. The spectra do not change extensively when the crystals are rotated around the axes shown in .Fig.l. The single crystal spectrum is shown in Fig.2. The most resolved spectrum taken at all orientations of the magnetic field in three

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320

a

b

KOKSAL, TAPRAMAZ, AND DULKAR

FIG.2. E.s.r. spectrum of gamma irradiated tetrabutylammonium iodide single crystal a)H//c, b)HlC 20' with the a axis.

orthogonal planes is shown in Fig.2b. The spectra do not change significantly between 140 and 350 K and therefore independent of temperature in this interval. The powder spectrum of tetrabutyl- ammonium bromide is given in Fig.3.

From the single crystal spectra of tetrabutylammonium iodide and others we infer that the g value is isotropic and g = 2.0030.

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TETRASUBSTITUTED AMMONIUM COMPOUNDS 321

10 G H

FIG.3. E.s.r. spectrum of tetrabutylammonium bromide powder.

These r e s u l t s i n d i c a t e t h a t t h e s p e c i e s r e s p o n s i b l e f o r these s p e c t r a should be an a l l y l - t y p e of r a d i c a l . Since t h e hyper f ine

s p l i t t i n g i s 1 4 gauss it cannot be a n a l k y l type of r a d i c a l .

I n a l k y l r a d i c a l s t h i s s p l i t t i n g i s around 23 gauss . The c a l c u l a t e d s p i n d e n s i t y d i s t r u b u t i o n i n a l l y l r a d i c a l , is given i n Table 1. It has been shown t h a t when t h e H atoms i n t h e a l l y l r a d i c a l are s u b s t i t u t e d by a l k y l groups, t h e 71 e l e c t r o n s t r u c t u r e does not change s i g n i f i c a n t l y 116-17 I . Consequently, we may expect t h a t t h e s p i n d e n s i t i e s on C C and

C atoms i n RR'-C" R'l*S($f1''R'II' r a d i c a l s must be r e s p e c t i v e l y , 0.6, -0.2 and 0.6, as i n t h e case of CH2=CH"-'CH2 r a d i c a l , but

t h e hyper f ine coupl ing c o n s t a n t s with f3 protons are a % 1 4 gauss and a 2 n 4 gauss. Here, one may expect hyper f ine s p l i t t i n g due t o hyperconjugat ion from i n t e r a c t i o n w i t h f3 protons of t h e a l k y l groups. However, t h e hyper f ine coupl ing c o n s t a n t s depend on t h e

Fipi''&H-&f2'

(1) ' ( 2 )

(3) (1) F2) 1 9 3

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322 KOKSAL, TAPRAMAZ, AND DULKAR

TABLE 1 Spin d e n s i t y d i s t r u b u t i o n s on C atoms i n t h e fiV zfl’#2 r a d i c a l 1 2 2

Ref. 61, CC) (5) Method o f c a l c u l a t i o n

Valence bond 0.67 -0.33 0.67 1 2 , 1 3 MO i n c l u d i n g c o n f i g u r a t i o n i n t . 0.6 -0.2 0.6 12 ,13

MO w i t h SCF 0.61 -0.18 0.61 14 MO Huckel approximation 0.5 0 0.5 - Experiment 0.58 -0.16 0.58 1.15

TABLE 2

ESR parameters of some a l l y l i c r a d i c a l s

Ref. Hyperf ine coupl ing c o n s t a n t s ( G ) Radica l

o r i e n t a t i o n of t h e f3 p r o t o n s r e l a t i v e t o t h e p, o r b i t a l of t h e

unpaired e l e c t r o n and t h e r e f o r e t h e v a l u e s of a must be lower

owing t o smaller v a l u e s of t h e s p i n d e n s i t y d i s t r i b u t i o n i n

Table 1.

B

The p o s s i b l e a l l y l i c r a d i c a l s known t h a t can f i t our s p e c t r a are g i v e n i n Table 2 w i t h t h e i r h y p e r f i n e c o u p l i n g c o n s t a n t s .

These i n d i c a t e t h a t our s p e c t r a should be t h e rne thyla l ly l r a d i c a l ,

@I - CH2. The l a r g e s t va lue of t h e h y p e r f i n e coupl ing

c o n s t a n t of t h e proton bound t o g) is 5 gauss as shown i n Fig.2b

and a t a l l of t h e o t h e r o r i e n t a t i o n s of t h e magnet ic f i e l d t h i s

3 8 FfI

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TETRASUBSTITUTED AMMONIUM COMPOUNDS 323

FIG.4. E.s.r. spectrum of u l t r a v i o l e t photolyzed (CH3)4NI powder.

s p l i t t i n g is less t h a n 5 gauss . The a n i s o t r o p i c p a r t of t h i s

coupl ing c o n s t a n t can be es t imated t o be 1.5 gauss. Both the gamma i r r a d i a t i o n and u l t r a v i o l e t p h o t o l y s i s produce

t h e same r a d i c a l i n tetrabutylammonium compounds, but i n t h e case of gamma i r r a d i a t i o n t h e radical l i v e s longer . The l i f e - t i m e is a few weeks i n t h e case of gamma i r r a d i a t i o n but a few days i n

t h e case of u l t r a v i o l e t photo lys i s . We could not grow t h e s i n g l e c r y s t a l s of tetrabutylammonium bromide and c h l o r i d e but s i n c e

their powder s p e c t r a are equal and t h e same of tetrabutylammonium

compounds and t h e r e f o r e t h e same r a d i c a l o c c u r s i n t h e s e subs tances dur ing gamma i r r a d i a t i o n and u l t r a v i o l e t photo lys i s .

We t h i n k t h a t t h e m e t h y l a l l y l r a d i c a l s are formed a f t e r d i s r u p t i o n of a b u t y l group from t h e N atom l i k e t h e formation of CH3 r a d i c a l from (CH3)4NI and (CH3)4PI as i n t h e fol lowing.

We could not observe any s i g n a l i n gamma i r r a d i a t e d (CH ) NI 3 4 and (CH3)4PI a t room temperature probably due t o uns tab leness of

t h e produced species, as w e do not have i n s i t u i r r a d i a t i o n

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324 KOKSAL, TAPRAMAZ, AND DULKAR

facilities. However, in situ ultraviolet photolysis of (CH3)4NI and (CH ) PI powders at 140 K produce CH3 radical which is easily recognizable from its ESR spectrum. The spectrum is characterized by its intensity pattern of 1:3:3:1 with a spacing of 22.5 gauss, as shown in Fig.4. The g value is 2.0037 and both the g and the hyperfine constant are isotropic and in agreement with the literature values (7-101 . We have also photolyzed a number of tetramethylammonium and phosphoniwn compounds (CH3I4NBr,

(CH314NPF6, (CH314NBF4, (cH3)4NHS04 , (CH3)4NC104 and (CH3I4PBr at the same conditions but we could not observe any signals after some hours of photolysis. However, the methylallyl radical in tetrabutylammonium compounds and CH3 radical in (CH3)4NI (CH3)4PI are observable in a minute of photolysis. This may indicate that one of the butyl groups in tetrasubstituted ammonium compounds, and one of the methyl groups in (CH3)4NI and (CH3)4PI is more strongly bounded to the surrounding lattice rather than to the N and P atoms.

3 4

ACKNOWLEWBENIS

This research was supported partly by the Research Fund .of Ondokuz Mayis University.

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TETRASUBSTITUTED AMMONIUM COMPOUNDS 325

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Date Received: 10/10/91 Date Accepted: 11/12/91

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