Conformational study of CH3OP(O)Cl2 and CD3OP(O)Cl2

doumol of Molecuhr Stnrcture, 125 (1984; Elsepier Science Pubhsbers B-V_, Amsterdam

CONFORMATIONAL

STUDY OF CH,OP(O)Cl,

Part 3. Low-temperature

G. H. PIETERS

243-251 -printed

m T%e Netherlands

AND CD,OP(O)Cl,

solid state and matrix isolation study

and B J VAN

DER VEKEN

Labomton-urn uoor Anogrmiuhe Scheikunde. R~krunkrsitair (R UCA). Groenen bogerlaan 171.2020 Antwerp (BeMum) A

Centmm Antwerpen

J. BARNES

Depariment

(G t. Britain)

T. S. LITTLE Department (Received

Chemistry and Applied Chemistry.

of

Uniuersity of Salford. Salford M5 4 WT

and J. R. DURIG

of Chemistq,

Uniuerslty

of So?rth Carohna, Cohrmbiq SC 29208

(USA.)

5 July 1984)

ABSTRACT The FIR, MIR and Ftaman spectra of methoxy dicbloropbosphinoxide and its deutented aualogue in the low-temperature solid state and the low-temperature matrix isolation MIR spectra of the normal compound have been recorded_ The previously published assignment of the deformation modes is slightly revised The tmns mnformer was found to he the only conformer left in the annealed solid state while the confonnational distribution trapped in the matrices is similar to the gas-phase equilibnum. INTRODUCTION

A recent liquid [l] and gas phase [2] vibrational and conformational analysis of methoxy dichlorophospbinoxide resulted in the assignment of the individual bands in conformational doublets to the gauche and fmns conformers. -4 temperature study of both phases [1, 33 and statistical thermodynamic considerations [3] resulted in a AH (Hgauche - Hhnr) between the gauche and tmns conformer equal to +2 9 f 0.3 kJ mol-’ for the liquid [ 11 and -2.1 f 1.5 kJ mol-’ for the gas phase [3]. H&rail [4] published low-temperature solid-phase MIR recordings for the skeletal stretching vibrations in the normal compound from which it was concluded that the more polar conformer is the more stable conformer in the solid phase. H&rail [4] however did not attempt a geometrical identification of the two conformers present in the liquid and gas phase. No results on other fundamentals were reported [4]. In order to complete the vibrational and conformational analysis of

CH30P(0)C12 and CD30P(0)C12, the low-temperature (77 K) solid phase was reinvestigated and a matrix isolation study performed_ 0022-2860/84/SO3.00

Q 1984

Elsevier

Science

Publidxers

B.V.

244

The nomenclature for the fundamentals proposed in ref- 1 is used in this text, with the exception of some low-kquency modes for which more appropriate descriptions are given. EXPEXIMENTAL

The compounds were prepared as described in ref. 5 and purified on a low-temperature Wtionation column [6]. Low-temperature solid-phase MIR spectra were obtained using a Digilah FTS14C Fourier Transfcnn interferometer equipped with a Ge/KBr bwmsplitter and a TGS detector. Low-temperature solid-phase FIR spectra were obtained using a Beclunann 720 Fourier Transform interferometer equipped with a 625 p Mylar beamsplitter and a Golay detector. The low-temperature solid-phase Raman spectra were recorded on a Gary model 82 spectrophotometer equipped with a Spectra Physics model 171 argon ion laser operating on the 5145 nm line. The MIR matrix isolation spectra of CHsOP(0)Cl, in Ar, N2 and Co matrices were recorded with a Perkin-Elmer 180 spectrometer. The solute/ matrix gas concentration ratio was eqr;yl to l/500 for all gas mixtures. The sp~rra of the solid state and matrices were recorded before and after annealing. All FIR and MlR spectra were recorded with a 1 cm-’ resolution, while the Raman spectra were recorded with resoiution up to 2 cm-‘. DWZLJSSION

Matrix isolation The assignments of the matrix isolation spectra of CH30P(0)C12 in Ar, CO and Nt-matrices are hsted in Table 1. The N2 matrix spectrum shows a band at 3045 and one at 3020 cm-’ which are assigned to the Y,(CH,) (a’, a”), while the other matrix spectra show only one band in this region. The spectra of the skeletal stretching fundamentals are shown in Fig. 1. From these it is clear that both conformers are present in the lowtemperature matrices and that, compared to the liquid and gas phase spectra [1, 21, the conformational distribution trapped in these matrices most closely resembles the gasphase equilibrium. A conformational doublet appears for the v(p--O) fundamental, which displayed only a single band in all other spectra of these compounds [l, 23. Further splittings of individual bands in Fig_ 1, and also for other fundamentals, are assigned to site-effects in the matrices since these splittings are not reproduced in the differem matrices and because they do not exhibit the expected isotopic intensity pattern for compounds containing two

245 TABIX

1

Low-temperature solid phase and matrix isolation spectra of CH,OP(O)CI,

3049

m

5057 VW

30499

3027

m

303lvw

3028s

2965s

2969 m

2965,x

3054s 3047s 3026 m 3022 m 2965 s

2860 m 2584m

2864 w 2598t-w 2578 w

2858s

2868m

2486 226-l 2222 1990 1352 1459 1459

302oIv

3045w

3020

3020

xv

2965 m 2930~ 2862~

3020 w w

3020

w

2970 m 2923~ 2865~

2962

m

a

v~
2665 v

see

s.br m a w s ts vg

1995w 1846m 1470s 1450 s

mbr

1314sh 1a9m 1298 l

1458 mebr 1458 m.br

1458 1458

m.br m.br

13oosh 1293s

1304m 12& s

1461 1446 1350

m 1463 m m 1446m w -1354 w

1461 m 1443m

1332

m

1327

text

1459 i- 004=2263 1162+1060=2222 1162+ 830=1992 1051+ 640=1855 6&H,) o'.S;(CH,I a' 6 (C9,) a* 1842+ 314=1356

22655

1324m

1300

1309 ll& 1162

vs sb

1051 1025

tx sh

11921x 1162s 1055sb 1047 vs

830 809 804 778

70i

'607 574 550

= w

1184 116u

VW VW

1049vw

1049

VW

103sda

1009

935 876

ll& ww 1160 s-w

5

1332

m

1321 * 1309s

11a3 m 1103 m 1078 m 1074 m 1059 m 10469 1042ts

1182 m 1182 P 1069 sb 1066 s

816 m 313 m

822 sh 819 m

805 m

608 m

1038 s 1032 w

=

933m 876~~

m m w w

816sb 808s

630 812

m m

m

1063 sh v(C-O)o'frmr 1067 5 1 1030 vs v(C-o)Ecluche 1026 1036 s 1 590+420=1010 515+420=935 515+ 358=873 817 m \ ,NP-o)gouche 807 m

vfP-o)o'tmns >

722 m 716 w

732 w 727 vw

612 vs

619 vs 616 v5

732 m 726 vt

W

m 'c3 m

IqP=o)dtrmrr

I SOB+ 517=1325 1319 m 1305s v@=O~gauche 1302s > 1186 m P'uxqo" 1182 m P'CH,)cl

595

sb

590 %¶

-595a 575vw

-580

VLU

542ww 515 417

vs m

520~ 515 a 42Om

369 358

s s

371s 362s

523~ 418s

523 418

VP 5

3719 360s

371 360

s s

590 w 581s

587 5

549s 546m 521 w 515 w

555 5

375k-a 366 vw 351 VW

417+ 358=775 175+549=724 175+546=721 2X 358=716

Vpzl,)U~

tmru

517 w

516 w

377 VW 367vw 356~

6@-o-C)dtnm. 379 vw 6(-P=O)o o P.muche 366 b-w 6~)o.o.P a"t-ana 357 vw 6
246

TABLE 1

(continued)

3zom

262 275 226

w v m

277 = 230 m 227m

275 228

m m

275 228

m m

314 272 272

w 318 b-it275 t-w 275

aAbbreviationsr ss- very strong; s: strong; mr medium; shr shouIder; o.o.p.: out of plane, i-p.: in plane.

Fig_ 1. Matris (d) v ,,(PCJ);

isolation MIR specha of CH,OP(O)Cl,_ n , band due to hgh vacuum oil.

w 320 b-w 279 1-w 279

-a 6cP-O)i.p.gouche b-w t-WZl,~~audre w r
w: weak;

(a) v(P=O).

VW: very weak;

(b)

v(C--O);

5r

broad;

(c) v(P-0).

chlorine atoms 1’73. Furthermore, isotopic splittings are only expected in fundamentals in which the chlorine atoms are major participants. ‘The relative integrated intensity in the v_(PCl& u(p--O) and v(C-0) confonnational doublets for the differents matrices is very similar and considered identical There vrere no changes in the relative intensities of these doublets upon annealing. The ,(P=O) region, shown in Fig. l(a), exhibits in all matrices a weak band near 135G cm-’ which is assigned to a combination band. The Armatrix spectrum shows in this region two more bands which are assigned to the v(P=O) conformational doublet, with the less intense component belonging to the tm~e conformer, consistent with previous assignments [l, 2). The Nz and CO matrix show, besides the combination band, three band6 of

247

which the one near 1320 cm” has a different intensity in the two spectra compared to the other bands in this region Since the conformation&l distribution in the Nz and CO matrix is, as mentioned above, practically identical, the band near 1320 cm” cannot be assigned to the v(P=O) of one of the conformers but must be assigned to a combination band. Since the intensity of this band is high and varies between the matrices, the combination must be in Fermi resonance with the v(P=O) of the gauche or trans conformer. The Fermidoublet intensities predicted for ‘he combination of the u(M) and v,(PCl,) for the trans conformer are fully consistent with the observed relative intensities and therefore this combination is suggested as causing the resonance. This same resonance was also discovered in spectra of some other phases of CH,OP(O)Cl, where an analogous assignment was proposed [ 11. Lowtempemture

solid state

The assignments of the low-temperature solid state MIR, FIR and Raman spectra of CH30P(0)CII and CD30P(0)C11 am lis+md in Tables 1 and 2, respectively. Both Raman and infrared recordings show band splittings which are not due to the existence of the two conformers. Again, as for the matrix isolation spectra, these cannot be assign& to isotopic splittings because of their irregular and non-reproducible appearance which lacks the expected zsotopic intensily patrem mentioned above. Therefore, and also because of the large number of lattice vibrational bands in the Raman spectra, these band splittings are thought to be caused by the existence of a complex lattice structure m the low-temperature solid state, with more than one molecule in the unit cell. The MIR recording of CD30P(0)C12 before annealing, shown in Fig. 2(a), displays bands near 670 and 561 cm-’ which are assigned to the PCl, stretching vibrations of the gauche conformer analogous to the assignments in the liquid and gas phase recordings [l, 21. After annealing these bands have disappeared, as is clear from Fig. 2(b). The bands near 1000 cm-‘, assigned to the gauche v(C-O), also disappear upon aulealing. From this it can be concluded that the t-runs conformer is the more stable conformer in the solid state and the only conformer left in the annealed crystalline phase. The MIR recording of the unannealed solid Elm of CHSOP(0)Cll was already free of the gauche conformer while the Raman spectrum of the unannealed solid state shows a very small fraction of the gauche conformer: the very weak band at 542 cm- i belongs to the symmetrical PCl, stretching vibration and disappears upon annealing. The FIR spectrum of the unannealed solid film of CH30P(0)Cls shows, amongst others, bands at 320, 282 and 130 cm-‘, which all disappear upon annealing, implying that they belong to the gauche conformer. The Ramsn spectrum of CD,OP(O)Cl, also shows very weak bands at 543 and 318 cm-’

248

TABLE

2

Solid state infrared and Raman spectra of CD,OP(O)Cl,’

3332

sh

3320 2680 2585 2485 2340 2296 2275

;v s s

br,s w sh sh

218'7 w

2147

2082 2074 2013 1965 1886 -1833 1520 1331 1305 1875 1255 1244 1220 1148 1107 lC65 1050 IO16 1010 1OOi 981

2275+ 1065=3340 2275+1050=3325 2x 1331=2662 2x l305=2610 seetext 1277+ 1065=2342 v;(CD,) up=(CD.) 0’ 1313 + 914=2227 2x 1107= 2214 2x 1065=2130 1108+1072=2180 1108+ 1055=2163

s

v-w VW w VW VW VW w m s vs sh sh m w vs vs vs

2294 2290

W

2294

S

2294

S

W

m

VW

W

solidCO, 1072~ 1055=2127

W

2274 2223 2215 2177 2165 2160 2142 2129 2102

S

2217 2183

2274 2223 221f! 2li7 2165 2160 2142 2129 2102

W

2x

2Oi5

S

2075

S

2142

2075 2G20 1960 1683 1830

W

VW

W

VW W W

x W

VW

v-w W W W W

I

VW VW W W

1318 1308 1290

1301 1295 1257

1185

W

1109 1065 1049

vs VS

vs

1108 1072 1055

w W 5

m W W

1318 1307 1290

1107 1072 1055

1055=2110

u,WD,) (1’ 1107+ 1050t llOi+ 1065+ 13051

913= 2020 913=1963 776-1883 776=1941 217=1522

W

-1 S

v(P=0)

m

2x 595 = 1190 776+ 367=1143 6I(CD,)a', a;(CW Y(C-o)O' tmra 6,wwd

W W

a’ f7utzs

S

vs vw s

913 396

s m

ii6

vs

i19

w

s(C-O) 920 916 900 771

s s

m vs

913

89i

775 766

m W m m

913 897 774 765

gauche

m I Ii 595+

125=720

a-

249 TABLE

2 (continued)

677 673 667

s

595

s

1

6

vs

606 595 586 581

vs

VS

S

515

403 401 367

2

401 403

iI

S

367

S

359

VS

5

272

w

272

w

217

S

217

S

177 125 65

m m S

177 125 65

‘Abbreviations: vs: broad; shr shoulder,

very

624

VS

m

S

VW

vs

561 524

359

624

m m

569 543 520 514 402 372 368 359 355 318 273 270 220 218 183 126

W

z V.S S

6

m m m m L W VW

S

shong;

SI strong;

w

520 514 402

I I 1 “1

372 388 359 355

6

m:

-I

570

sll vs

u,(PQ)

a” tmns

YJPC~) Y,(PC\)

gauche a’ tlnnr

6

6 (-)

li tI-a?LS

s

6 (-0)

0.0.p.

6 (P=O)

i-p_ 0’ tmns

a” tmns

S

m

m m

273 270 220 218 183 126 61 48 38 34 22

3

medium;

w

ip. gauche u” tmns

6 (PCb)

a’ tmns

1

W Sh

6 (P=O) r(PC\)

>

W

w (PCI,)

VW

r(C%) ar(PUC) G” tr0n.S lattice modes

W

weak,

a’ tmns

VW: very

weak;

brr

o 0-p. I out of plane, ip. I in plane.

before annealing. After annealing both disappear and are thus assigned to the gauche conformer_ Due to the additional mformation obtained in this study on the deformathe previous assignments [1, 23 of the tion region below 500 cm-l, deformation modes had to be revised. Previous assignments were based on a C,, model However, after careful comparison of the solid state frequencies of the normal and deuterated compound with the vibrational assignments of the difluoro compound that have recently become available [S] , it b-e clear that some of the normal mods had tc be redtied in terms of other local&xl modes, while for two modes the symmetry species had to be reversed_ The new assignments are pre.senM in Tables 1 and 2. It should be remarked that the ratio of the &quencies observed for the

250

Fig. 2 Solid shte Am

spectra of CD,OP(O)CI,

; (a) before annealmg; (b) after annealing.

normal and deuterated derivatives for the r(CHJ) is snaller than expected, ) the r&o is too high. This, howwhile for the band assigned to 7(P-O-C ever, can be explained by the coupling that has to occur between these modes, which is further substantiated by the relative intensities in these bands The MIFt recordings of both compounds exhibit z broad intense band near 2485 cm-l before znneahng. This structure disappears upon annealing. It is our belief that this structure represents overtones of the P=O stretching vibration which, as shown in Fig_ 2(a), has a very complex sbuctan-e before annealing. CONCLUSIONS A vibrational analysis of the low-temperature (77 K) solid state spectra of methoxy dichlorophosphinoxide and its deuterated analogue, and the makix isolation MIR spectza of the normal compound has been proposed. The previously published assignment [ 1, 21 of the deformation region had to be slightly revised. The matrix isolation spectra show conformational doublets and the

251

conformational d.i&ibution trapped in the matrices is very similar to the gasphase equilibrium. The frur2.sconformer is the only conformer present in the annealed crystalline state. The large number of lattice modes and additional splittings in bands in the solid-state spectra imply a complex crystal structure in the lowtemperature solid state for which at least two molecules are present in the crystallographic unit celL ACKNOWLIZDG

EMENTS

The NATO Scientific Affairs Division is thanked for Research Grant No. 569-82 and the National Fends voor Wetenschappelijk Ondenoek (NFWO), the RiJksuniversiti Centrum of Antwerp and the British Council are thanked for financial support. REFERENCES 1 G. H. Pieters, B. J. Van der Veken and M. A Herman J. MoL Struct., 102 (1983) 2 G. H. Pieters, B. J. Vnn der V&en and M. A. Herman J. MoL Stmct, 102 (1983) 3 G. H. Pieteq PbD. Thes& University of Antwerp, 4 F. Hemil, C.R. Acad. Sci. Paris, 261(1965) 3375.

27. 221.

1984.

5 K. Sass? (Ed.),

Methode Der Organische Chemie, Vol. 12, Georg Thieme Verlag, Stuttgart 1964, p. 213. 6 D. F. Shriver, The Manipulation of &sensitive Compounds, McGraw-Hill. New York, 1969. 7 J. Shamir, B. J. Van der Veken, M A. Herman and R. Rafaeloff, J. Raman Spectrosc, ll(3) 8 G. H

(1981) Pieters,

215. B. J. Van

der Veken,

J. R. Durig

and A. J. Barnes,

to be published.