&cdm&hh A~ta. Vol. 26A. pp. 1861 to 1866. Permmon Pfam 1970. Printed in Northern I=hrd

In-plane ~~~ frequeneie8 of six beak

deuterated biphenyls

#. ZIUZBI

Istituto di Chimiom delle Mwromolecole de1 C.N.R., Via A. Corti, 12 Miho, Italy

and

s. SAXDaoHI Department of Chemistry, Euratom Joint Reeesrch Cent&r, Ispre, Vareae, Italy

(&c&al 6 &brtuwy 1969)

Abk&--!l!he vibration& spe&re of six symnMri&y deuW&ed biphenyls were reported in the libture pxeviously, but were interpreted only qualitatively beoause of the oomplexity of the moleoulea and the peuoity of the experikental deta neoeaaary for a reliable assignment.

We present here the interpretation of the vibrational speotw of thaw moleales baaed on a sero-order normal oo-ordinate oaloulation, whioh adopts e mod&d Urey-Bradley foroe field previously derived by u8 from a least square oaloulation on biphenyl and biphenyl-d,,. Our snalyaie is reatrioted to the in-plane fimdamentals. Zero order ct&ulati fimdamentisl frequen- eiea f& those observed ukxely.

MUCH work has been carried out in our laboratories on the vibrational speotra of biphenyls sud severs1 polyphenyls, in the hope of obtaining informtition about their molecul&r vibrations. From a previous analysis of the ~b~tion~ spectra of biphenyl and biphenyl-& most of the fundamental vibrations were looated [I]. The detailed description of the normal modes (i.e. the vibrationaJ assigmnent) was obtained by a least square refinement of a simplified valence foroe field and a modified Urey-Bradley force field [Z]. The validity of the numbers obtained w&a discussed critically. It was concluded [2] that the information derived on the stru&zre of the molscnfe and on its normal ~b~tio~ ww f&y reliable, at least within the limits of our present technical ottpability of making a vibrational analysis in the harmonic approximation for a complex polyatomic molecule.

The possibility of predicting, by a zero-order cdoulation, the location of the funtimenttal vibmtional frequencies of isotopically substituted derivatives provides & further check of the usefuluess of the force field proposed. Since the preparation of sever&l ~et~c~~y deuterated biphenyls w&s described recently [3], rend the infrared and Raman spectra of these compounds were also reported, together with some qualitative interpretation [4], it seemed desirable to test the interpretation of the spectra on the basis of a normal co-ordinate calculation whioh adopts the force field already reported by us [2].

[l] G. !&mm and S. SANDROXX, ~~~~~~. A& MA, 483 (1968). [2] G. &RBI end 8. SANDBOXI, &ec8ruchim. Aota 2SA, 611 (1968). [3] F. Gxws, 8. SAND~ONI end G. Brxnx, J. lkxbdkd C3mpowA 8,271 (1967). [4] 5. SANDRONI and F. GEIMI, Spectmcti~. Aotu $82,236 (1966).

19811

Teblel. Calculatedandobservedin-plenefundamentslsforbiphenylanddeuter8tedderiv8tiveebaaed

on 8 26 parameter Frey-Brsdley

force field

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WW,W

WV',(~)

C,,H

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%&W,IN)

C,GW,

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ObS.

talc.

obs.

cd

c.

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oal

o.

obs.

cd

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oba

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blc.

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do.

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. do.

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s.

A,

spec

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Ram

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acti

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pol.

1 3032

3031

3077

2

3075

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3073

l

3072

3

3072

2269

2271

4

1615

1612

1614

1606

1692

5

1507

1507

1600

1500

1468

6

1281

1285

1281

1287

1240

7

1168

1190

1168

1198

1082

8

1024

1030

1013

n.0

. 982

9

996

1003

986

989

859

10

737

742

734

740

716

11

293

315

289

310

286

Brn

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R

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ac

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, dep

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1

3077

3079

3071

2

3070

l

3070

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3

1585

1695

1678

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1568

4

1462

1452

1444

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. 1440

6

1372

1376

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6

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1316

1301

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. 1240

7

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1158

1126

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. 1143

8

1071

1090

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846

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9

603

613

602

610

694

10

394

407

391

410

376

* 3077

3072

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1596

1611

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832

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712

709

700

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312

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1166

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3070

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1574

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1353

1276

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693

383

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sh.

n.0

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.

606

386

3074

2277

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1590

1461

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827

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3076

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832

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2280

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and C

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stm

t&in

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lect

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n o

ur

oom

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n

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=

not

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ign

ed.

sh =

sh

ould

er.

1964 G. ZERBI and 8. SANDRONI

The experiments1 snd c&r&ted infrared and Reman spectra, of the six possible symmetrioslly deutemted biphenyls sre now compared. The following compounds were studied.*

4,4’Biphenyl-&, (I) 3,5,3’,6’Biphenyld, (II) 2,6,2’,6’Biphenyl-d, (III) 2,4,6,2’,4’,6’Biphenyl-d, (IV) 3,4,6,3’,4’,6’Biphenyl-& (V) 2,3,5,6,2’,3’,6’,6’Biphenyl-& (VI)

CALCULaTIONS

In Ref. [2] both s simplified valence force field snd s mod&xl Urey-Brsdley force field for biphenyl were determined and discussed. In the present work we present only the results of the cslculstions bssed on e 26 parameter MUl3FF discussed in Ref. [2]. Zero order calculations were csrried out on a IBM 7094 computer and no refinement hss been attempted. Since the vibrational ape&rum is not very sensitive [l] to the possible slight rot&ion of the two rings sround the C-C bond that occurs in solution [6,6], calculations were carried out by sssuming the two rings to be coplanar ss they sre found in the crystalline state [7, S].

The irreducible representation corresponding to the D, point group contsins 11

A, and 10 B,, R&man active, 10 B,, and 10 B,, infrared ective in-plane normal modes. The geometrical parameters adopted and the symmetry co-ordinstes used are fully described in Ref. [2].

RESULTS AND DISCUSSION

When the caIcul&ed fundamental frequencies hsve been obtained from the computer, the process of selecting the experimentally observed bands from s compli- cated spectrum of s complex polyatomio molecule, such ss those studied here, is not straightforward. It is now admitted thtlt when two fundsme&& of different sym- metry species occur at close frequencies an assignment bssed only on c&u&ion is very doubtful. The introduction in the force field of enother inters&ion constant mrty well switch the order of the species. Since the force fields used are always very approximate, the fitting between calculated snd experiments1 frequencies csn be objectively and reliably judged only when other experiments1 data can be collected on the species of vibrations which give rise to infrared absorption or Ramsn scatter- ing.

Depolsrization rstios of Ram&n lines, bsnd shapes for the vspours, dichroic measurements on oriented samples or single crystclls in the infrared, and data from the electronic spectra sre needed.

*For the atom numbering sue Ref. [a].

[6] H. SUZUKI, Bd?. Olwn. Sot. Japan 82,134O (1969). [0] H. H. Jti and M. ORUFUN, Theoq wad AppK.cu&nw of Ultmwiolet Spectrosco~. John

Wiley (1962). [7] A. HAlK3RBAV.W and 8. H. Rrzvr, Aota @yUt. 16, 366 (1962). [S] J. =a, Acta Oryst. 14, 1136 (1961).

~~+ane fundamental ftecpuoies of six ~et~~~~ ~~UIXXYH& biphenyis 19m

JVhea fewer OF no otherr ex~~mental data are ava~able in addition to the simple infrared and Rmna~ spectra, creation based on critically deemed force fiefde may be used &B & very gmd indhtion of the location of the ~~rnenta~ sought. The criteria generally adopted when correlations ar8 carried out on the spectra of similar molecules may help qualitatively in identifying the nature (i.e. speoies) of the vibrationa involv8d. When no strong vibrational perturbation are introduced by the aub&ituent, the intensity of some bands is man&a&d throughout a aeriee of chemi- sally similar ~orn~o~~, thus ~~ the ~o~~a~~n between observed and cal- culated frequencies.

Sirme, for the moleoules studied in this work, the experimental data are very few, we have baaed our choice on the following criteria:

(a) The calculated A, fr8quen&s should correspond to polarised Raman lint. (b) The intensities of the bands throughout the aerie@ should be roughly eom-

parable. (0) Comparison between. the sp8etra of single cry&al and unoriented samples in

KBr pellets. Because of the orientation of the molecule with respect of the face of the single orystal, dichroic measurements do not help in deciding the dire&ion of the dipole moment change (1, QJ.

Since the tbre8 conditions above have been nicely fuEll8d by at least 60% of the 186 calculated fmquenei8f3 (60 C--K or c--T) stretcfrings ar8 obviously ne&&ed) we conclude that the fit between calculated and observed frequencies can be eon&&red ~t~f~to~. The vibrational ~i~rnent thus derived (i.e. the choice of the species and the def&ption of the mode as obtained from pot+&ial energy ~t~bution), ia fairly n&able even if not certain. Whether or not two difEer8nt force flefda, say UBFF and X?l?F$ give app~~a~ly the same deecription of the normal modes is still open to qu~ion, and must be first de&led on small8r molecules.

c0I?oLIJs10ws

On the baaia of the experimental data available in the previaus literature only, the vibrational assignment for the six symmetrically deut8rated biph8nyls could not be props. The G~~~atious reported her8, based upon the chmn foroe, field have provided a fairly refiabI8 indication of the location of the in-plan8 fundamentals and their description The sati&otory fmquen~y fitting only using a z8ro order calcula- tion provides further support to the ~~ab~ty of the proposed fore8 field derived in the harmonic app~~mati~n with a least square &inement. No attempt w&8 made to in&de all the data obtain8d from the computer output nor to aualyxe them in the text. All listings (Fo~nti~ energy ~t~buti~ mat&es, fan ~pIa~ment, Jacobian matrices etc.) are filed in our laboratory. Copies are avaiIabIe upon request.

AdrmA-dgmbWe thank Dr. H. HANWAXBT, Dr. F. GEISS, Prof. G. NATEA md Dr. IL &fAN!r.ICA for the interest they have &own in our work.

f9] S. cALKBAETO,J,~ftesrp. p?38.%$,903 {1992).