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Electron diffraction study of the molecular structure and conformation of gaseous 2-furoyl chloride
Jourz;cJ ofMolecular Sticture, 136 (1985) Elsevier Science Publishers B-V., tisterdam
25+262 -Printed
m The Netherlands
ELECTRON DIFFK4CTION STLTDY OF THZ MOLECULAR S’I’RUeCWFtE AND CQhTORMATION OF GASEOUS 2-FIJROYL CrnORPDE
KOLBJBRN
HAGEN
DepaTtment (Received
of Chemism. 12 February
A’YH,
Univemzty
of Trondherw.
N-7000
Tror.dhelm
(Xoruray)
1983)
ABSTRACT The molecular structure of 2-furoyi c3loride has been invest:gated by gas-phase electron diffraction at 86” C Two du%inci conformers vrert identified, a more stable plenar Form with the furen oxygen and the czrbonyl oxygen syn and a less stable planar (or nearly p1ene.r) anti form_ Avummg that --he ho fcrms differ m their geometies ocly in fie O=C--C-O rorslon angles and vsurning the furan ring to bale Czv symmetry, the results for some of the d&Lances (ra) and angles (F,) are: r(C-I-I) = 1.110(20) X, r(C=O) - 1 ZOi(6) x, r(C-0) = 1378(10) L, r(C-cot X, tr(C-C)) (average i’ = 1,465(X3) cerbon--carbon distance in the furen r.ng) = 1 392(S) X dr(C-C) (difference befnveen single and double carbon--carbon distances m the furan nng) = 0.069 X (assumed), r(CC1) = 178’i(6) X, LC=C-COCI = 131 6(S)“, rC=CI-G = 110 S(4)", r-C=C-H = 127 7(13.4)“, .L~C=O = 125 S(8)” 2nd LC+C’-C~ = 111 S(6)” At 359 K the observed amount of the conformer wi+ch tne oxygen a&cornssyn was 69 8(14 2)E INTRODUCTION
Most conjugated acid chlorides such es 2propenoyl chlonde [l] , tram-Zbutenoyl chlorrde [2] and fumaryl chlorrde 131 are fo-und to exist rn d-12 gas phase as rmxtures of ro+tatronal isomers. One exception is 3-methyl-2-butinoyl chlonde whrch is reported as havrng oniy one form 2-Furoy: chlorrde (Fig. I) IS another mo’lecule of the sane type in which rotational isomerrsm might be possrble. The structure of the correspondmg aldehyde, 2-furaldehyde, has been extensively studred 14-133 and the results show that in the Iiauid and gas states two conformers with either syn or anti oxygen atoms coexist Less work has been reported on 2furoyl chloride; two spectroscopic studies 114, 151 indicate the presence of both syn and anti conformers and theoretical -X0caiculations El61 have given an energy difference between the conformers of 3 0 kcal mol-‘, the form with the oxygen aAtoms mtr having the lowest energy. Gas phase eiecxon tifiactlon gives, m addnion to bond distances and valence angles, mformatron ahout 30th tYne amount and type of conformers prewnt, and we report here the results of such an investrgatron
0022-2860/85/SO3.80
0 1985
Elsevier
Science
Publishers
B V.
256
Fig
1 Diagram
EXPEEIMENTAL
oi cotion?lers of 2-Euroyl chlorde. AND
DATA
REDUCTION
2-F-uroyl c_hloride (>98%) was obtamed from Fluka AG The sample purity was checked by GC before use. IX!fraction photographs were made on Kodak Electron Irnzge plates in thtl R-hers Eldlgraph KDG-2 117, I.83 at theuniversrty ofGs10, with a nozzletip temperature of 359 K. Three plates horn the long (50.012 cm) and srx frc n the short (25.012 cm) nozzle-to-plate distances were selected for an lysis. Tne electron wavelength was c&bra&d agmst benzene [19]. The prr cedures for obtammg the to’tel scattered mtenslty drstrrbution (@I,(s)> ant the molecular mt=znslty (d,(s)) have been described pre-xtoudy [20-221. Data from the long and short camera distances were obtained over the ranges 2 00 < s < 15.00 and 5 00 < s < 28.50 A-‘, respectively, 2~ mtervals As = 0.25 A4. The avenge experimental intensity curves are shown m Fig. 2, the Ir_drvrdual cumes end backgrounds ere avarIable as supplementary maternal [23]_ Electron scattering ampLi%udes and &as-e shrfts were calculated using Hartree-Fock potenti& [ 24, 1 for C, 0 uld CL, while molecular bonded potentials were used for H [25] STRUCTURE
ANALYSIS
An experimental rad~A distribution (RD) curve (Fig 3) was c&A.ated in c the function IA(s) = Sr,(s) the usual way by the Fourier transformation oA Z,Z,A~'A~ - exp (-Bs*) with 3 = 0.0025 A= Theoretical RD-curves were c&culated for conformers with the two oxygen atoms syn (a = 0” ) or czrrZr (a = 180” ) to each other, usmg reasonable values for bond distances and valence mgies. The torsion sensrtive drstmces are aLLlarger th-a 2.8 _A, and the outer part of the experimental RIB-curve is shown in P:g. 4 ‘together v&h theoretical curves for tie two conformers From these curves it was obvious that the major conformer was that vt-&&the oxygen at~~m!~S-JW However, the two theoretrcal curves ere not very d3fferent and some of the ant1 form m2y also be present Refinements of tie structure were czrrred out Ly the least-squares method [26l based on mtensrty curves by adjustmg one t~eoretr~4 curve to the *O average experL.menti curves (one each from the long 2nd short camera dir+ tances) using a urn6 wei@lt matrix. _Assuming the two conformers to have
357
I
I
0
I 4
1’ .;
5
:5
Fig. 2 Intens~ky cu_‘~es, d,(s) fo, rhr two camera dlsmces. in Table 1 Differeccc cnrve
b-------..
0
1
.
‘..
“’
%A-1
’ 30
Experlnental curves (Ex 1, Ek 2) are avs- ages of ali p!azs Theoretical curve (Th ) TX ~Aulated Go n CL= parmebrs (Di 1, Di 2) are Xx.-Th
‘1.
:
i5
&I
‘1
5
.
.
I
i
R,A
/i
Fig 3. Radnl distzbution cu~yes The experimental curve (Es.) IS calculated from the composite of the experizenti cum* of Fig 2 af+zr multlphcation by Z&~_,JA&a with E damgmg coefficient B = 0.0025 X’ and ~lth theoretical claka for 3 < s < 2.00 A-’ Ti;e tieorekzal curve (Th ) corresponds to the model of Tab!e 1 T3e di’ference curve (DC) 1s experimental minus theoretical.
radial distr!butio3 tunes for the conformers ir-ith the oxygen atoms FE 4 Theoretxal syn or anti together with the experimental curve Only the confoxmationally important parts of the curves are shown
equal geometry apart from the O-C-C=0 torsion angle Q, and assummg ‘he furan r-mg to have CZr-symmetry, the structure of 2-furoyl chloride can be described by 13 gecmetrrcal parameters, in our refinements taken as- r(C-H), r(C=O), (r(C-C)) = 0_5(r(C,=C,) r(C2-&)), L.r(C-C) = r(Cz-C3) r(C1=Cz), r(C -0). r(C,--C,), r(C-C!), LC,-CI=C, ILc2=ci*, LC=C-H. LC-C=O, LC-C-Cl and 0, the O=C-C-O torsion angle. Calculations of v,brationA amplitildes (1), perpendicular amphtr;dc corrections (K) and cenm*Jgti distortion constants (0) were carried out using a valence force field which was combmed from valence force fields of furan [27] and propenoyl chloride [27] _ In the least-squares refinements the vibrational amplitudes were kept constant at the calculated values. For the carbon-carbon bon& in the furan ring an accurate value for the average bond length could be de-ermined. However. the difference between r(C-C) and r(C=C) was tificuito determine due to overlapping peaks m the RD-curve In the tial refi-lemanz; this difference was therefore kept constant at the value (0.069 A) observed in a microwave spectroscopy invesfigation of the furan molecule [28]_ Tests showed that ‘Se U-C-C=0 torsion angle m the form v&h the oxygen a’toms syn, & 1, had z-o be close to O”, and in the final refinement it was assumed to have this value. In this final refmement srx distance parameters, six angle parameters and the conformational comPostion were refined sunultaneously. The fin& reslults are grven ti Table 1
259 TASLE Final
1 parameter
Parameter i( C-E) r(C=O)
r(C-0)
tic,-&)
v&es
for the structure
rafkI l.ilO(20) 1 207(6) 1 378(10) 1 465(X!) i.392(8)
LC=C-H LC-c=o L C-C-CI @Id GtC % syn
(0 C] 153.2111.6) 69.5(14.2)
c,=c,-c,
,Lc=c-0
0.076 0 039 0 046 0 04s
[0.069] l-787(6) 131 S(9) 110 9(4) 127 7(13 4) 125 818) 111 8(6)
L
&I,
0 051
Selected dependent angles and distances L c, =c,-C, 106 3(3] :c-O-c 105 6(6J L WC-c 117.1(B) Lc=C-Cl 122 5(i) r(C=C) 1357(8) 0 043 r(C,-C,) 1426(8) 0 048 ‘(C, - C5) 2 225(a) 0 952 r(C; - C, 1 2 569(11) 0 064 r(C: - 0,) 2.257(7) 0 050 r(C, - 0,) 2.427<13) 0 c71 r(C, - c, 1 2 183(10) 0 052
of 2-furnyl
chkwulea
Parameter
r( c, - o-) r(C_ - Cl)
r(C, - c, 1 tic, *C,! r(O_- cl) r(c, - Cl) r( c; - Cl’1
7
‘(C; - Cl) q 0, - Cl) r(C: - 0,)
r(C, - G-) tic,- “-) 40-O) r(Y, - Cl)
b OOsyn
r(H,
- Cl) r(H, - ClJ
r(C= ‘(C, r(C, r(0, r(C, r!C, r(C,
- Cl) - Cl) - Cl) -Cl) * O_) - o-) 0,)
J
00 CmCz
1s 0-L Cl) ) r(H, - Cl) I r(H, - Cl>) rl0
0)
2 362(11) 2 695(12) 3.670(10) 3 559(9) 2 620(9) S.OSO(lSj 4 487\16) 4.844(13) 3 9Sl(ll) 3 633(1-g) 4 V6(12) A 124j12) 2 603(16) 2 851(254) 5.323( 104) 5 913(41) 3.985(25 J -l 760(15] 4 196(33) 2 869(76) 3 OS9(211 4.367(14) 4_51S(!S) 3 500(2i)
0 CSi
4_WS(153) 5.843(21) 4 907(143)
0 134 0 123 0.164
0 076 0.060 0 064 0 C65 0.127 0.120 0 059 0 077 0.065 0 076 0 10’ 0 109 0 212 0 165 0 113 0 076 0.101 0.133 0 133 0 102 0.091 0 GiO 0 069
r aD:stacces (r,) and v:brawonaJ LTplltudes (1) are L-I Angs~-roms, mgis 1~ degrees. Parenthcsrzed uncertainties are 2r ana include estimates of systsmat:c errors and corre!akion m the experimental data. Quantitres m square brackets were kept cons-ant in the final refmement. b(r(C-C), = 0_5[r(C,=C,) I r(C,-C,)] ‘ar(C-C) = r(Cz-C1) - r(CI=C_)d*l is the O=*C-0 torsion angle of the conformer where the two oxygen atoms are syn &toeach other e+z is the O=C-C-C torsion angle in the anti conformer
and theoretical intensity and RD-curves cakulazd shown in Figs 2 and 3 toget!~r with difference matnx is gwen in Table 2.
from cures.
these results are The ccrrel2tion
DIsCLLsSION
Our investigation of gas phase Z-furoyl chlonde shows that the conformer rxtith the C=O and C=C double bonds antr to each other (oxygen atoms ~yrr) are the most stable. The same was also observed for 2-propenoy: chlcrlde
260
TABLE
2
Correlation
1 WC-c)) 2 r(c--01 3 rcc-H) 4 r(C,-q) 5r(C=O) 6 r
UStandard
matrix
x 100
0-a
71
0.0019 00023 00049 00031 0.0014 0.0013 029 0.15 4.45 0.27 0.20 3.86 a 74
iO0
deviatmn
for the r1 -S 100
ptrame&ersof 2-furoyl ‘3
r4
rs
=6
-24 21 100
1 -3 -13 100
2 13 a -41 100
-8 9 10 -35 6 1oJ
from leastsquares
refinem
chloride L-
-42 45 15 -31 15 26 100
4 -12
4
L,, 4
3-4 -7 24 57 4 -29 4 -30 6 46 -1 100 23 100
LII
3 -7 2 2 11 -10 -35 -1 21 7 53-m 49 -1 -30 3 28 -27 1co -60 1CO
4,
‘5.3,”
23 28 -23 -8 11 24 -30 -23 8 0 4 3 10 -31 -10 15 46 17 49 -2 -37 -12 100 0 100
mts
[l] . Our results are the-&ore in disagreement with the theoretrcal JMO-calculations [16] E we assume the two conformers of 2-furoyl chloride to have approxrmately the same entiopy, the observed conformational composition corresponds to an energy difference of about 6 6 kcai mol-‘_ This is slightly higher than the value observed ;O 3 -t 0.4 kcal mol-‘) for propenoyl chloride ]I] In 2-furaldehyde the csnformer with the oxygen atolms s;zti (G=C and C=O syn) was observed to be the most abundant form in the gas phase wi’& 69(g)% present at 323 K 141, correspondmg to an energy difference of -0.5 = 0.4 kcal mol-’ between 00 s3n and 00 cntr. Therefore, while 2-furoyl chloride and propenoyl chloride have smular conformational properties, 2-furaldehyde and propenal are very drfferent since propenal m the gas phase exists predomirzntly as a conformer with C=C and C=O anti [29, 303. It would appear thet m attraction exists m 2-fureldehyde between the furan oxygen and the aldehyde hydrogen, which stabilizes the conformer wn91 C=C and C=O vn. In Table 1 we have reported a torsion angle of 153(12)” for the high-energy form of 2-furoyl chlorde. This was the result obtained when a torsronahy stiff model was used for this conformer. However, our data arc also consistent with a planar conformer undergoing large torsionai motion or WIG-I a mode! havmg a low torsional barer at the planar no&ion The electron dl!fraction experiment cannot distinguish between these possibilities. In a possrble pianar form of this Qpe, the distance between the chlorine and the furan oxygen will be very short, and it is therefore not unlikely that a small hump exLct.s m the torsional potential function at & = lE!O” _ In Table 3 the geometrical parameters of 2-furoyl chloride are compared with those for some related molecilles. The geometry of the furan Lug is not much changed by the presence of the COCl group_ Valence ares and bond distances are ve_ry simrlar in furan and 2-furoyl chloride, and 2-furaldehyde
261
TABLE
3
Geometry
of furoyl
chloride
P-Furoyl
and
some
chloride
relntid
moleculesa
2-Fur-zldehyde
Furz n
P -openoyl
LC, =c,-c, Lc,=c,--o
i-207(6) 1.787(6) i 465(13) 1357(B) 1 42618) 1.378(101 131 6(9) 125 E(8) 106.3(3) 110 9(4)
1.453[71 [l-361] [ 1- 4311 [1362] 131 7(d) 122.7(S) Cl06 I] [i10.7]
106 07(2) 110 65(2)
LC-O-C
105
[lo6
106_56(
l-(C=O)
tic--c11 4c-G 1 r(C=c)
tic,--c, 1 tic--o) Lcl=c,-c, LC-c-o
Dls+ace Ref
types
8(8)
ra This work
=Dlstances in _4ngstroms, meanrngs in the ddFerent
1.192(2) I78S(j1 1.484(4) 1339(2)
1_212(4)
ra 4
51
chloride
1 3610(3) i 4301(5) l-3622(2)
123.4(7) 125 2(Z)
rs
38
2) 7a 1
angles in degrees Parenthesized tir cartamtiea may have different investigations. Quantxties in squarc~ bra&s& were -Gumed
and 2-furoyl chloride also have similar geometries. LC--C=O is larger in 2-furoyl chloride, but thk is often obserr;el for ac_d chiondes relative to the aldehydes. From Tab!e 3 11; can also be seen that the C=O ad C=C double bonds are longer and the C-C smgle bond is shon;e - in 2-furoyl chloride than ti propenoyl chloride, mdlcating that conjugation is more important m 2-fiiroyl chloride. ACKNOWLEDGZMENTS
We are grateful to Slv.mg. R Selp for help in recordmg *he electroE diffraction data and to Ms. S. Gundersen for +te&nkal ass;stance. Fmax~cxzl support from the Norwegm Research Council fo1 Science and the Humanities is gratefully acknowledged REFERENCES 1 2 3 4 5 6 7 8 9
K Hagen 2nd K. Hedbxg, J Am_ Chem. Sot , 106 (1984) 6151, T. NordrQmne and K Hagen, J_ Mel Struct , 128 (1985j 127 K. Hager J MoL St=&, 128 (i985) 139. G Schultz, I. Fe&g&~. &I_ Kolonits, A. I. Kiss, B Pets and J. B+&, J. Mol. Strlrct , 50 (1978) 325 J. M. Angelielli, A R Katn’zky, R. F. Prnzelh and R D Topsom, Tetrahedron, 28 (1972) 2037. D J. Chadwick, J Chem Sot Perkin Tz%. 2, (1976) 451. R. 3. Abrzharn and D J. Chadwick, Tetrahedron, 35 (19;32) la85 G. J- Karabatsos rad F. M. Vane, J _A! Chem_ SIX., 85 (1963) 3886. D Z Chadwick, J_ Ch-dnbers, G. D Meakins and R L EnoKden, J Chem. Sot Perhn Tr2n.s 2, (1975) 13.
262
1OK i Dahlquist and S_ Fonsen, J Psyr Chern, 69 (1965) 1760. 11 F. hI&nrug, H. Dreizler and H. D Rudolph, Z. Naturforsch.. Teil A, SO (1955) 1323. C Riche az~d C Pascard-Brlly, Tekabedron, 26 (1970) 12B Roqucs, 9. Combrisson, 3555 13 R J. Abraham and T. IV%Sivems, Tetmbedron, 38 (1972) 30315. 14 G Cassanas-Fabre and L Ranier. J. Mol Struck, 25 (1975) 281. 15 D J Chadwrck, J Cnarnbera, G D Me&ii and R. L Snowcien, J. Chem Sot Perkin TEXIS. 2, (1976) 1. 16 I. Lee and S C. Kun, J, Koran Chem. Sot.. 21 (1977) 32_ 17 W. !&ii, J Haze and L Wegmann, Z. Instrurnentenkd ,74 (1966) 84 1.8 0 Bastranaen. R. G_mber and L Weg-rnw Bakers High Vat Rep.. 25 (1969) 1. 19 K Tamagawe, T. Irjima and M. I&mum, J. Mel Struct ,30 (1976) 243. 20K Hagen and K Hedberg, J Am. Chem Sot , 95 (1973) 1003. 21 G. Gundersen and I(_ -ledbeg, J_ Chem Phys., 51 (1969) 2X0. 22 L Hedberg, _4bstrac’s, 5th Austm Symp. on Gas Ph-de Molecular Structure, Austin, T,X March 1974, p_ 37. 23 Available Eom B L L D. as Supplementary Pubhcation No. S ‘L; P. 26286 (4 pages). 24 T. G Strand and R A Bonham, J. Chem. Phya, 40 (1964) 1686 25 R F Stewut, E R. David-n and W. T’. Simpson, J Chem Phys, 42 (1965) 3175 26 K. Hedoerg and b: Iwasaki, Acta Crystallogr , 17 (1964) 529 27 L. Mann&r and ?u: 3 Phibbs, Analysis of Rarnan and Infrared Spectra of anjugated Molecules, Du Pont of Canada Ltd Research Center, Krngston, Ontario, 1975 28r’. Ma’& M. C Xkrta and G_ 3. S&nsan, J. Mol Srruct , 48 (1978) 157. 29 M. ‘lkerteberg, Acta Chem_ &and, 24 (1970) 373 30K Kuchitsu,T. F~Lxqvs~eand Y. Monno, d Mol. Struct , 1 (1968)463.
25+262 -Printed
m The Netherlands
ELECTRON DIFFK4CTION STLTDY OF THZ MOLECULAR S’I’RUeCWFtE AND CQhTORMATION OF GASEOUS 2-FIJROYL CrnORPDE
KOLBJBRN
HAGEN
DepaTtment (Received
of Chemism. 12 February
A’YH,
Univemzty
of Trondherw.
N-7000
Tror.dhelm
(Xoruray)
1983)
ABSTRACT The molecular structure of 2-furoyi c3loride has been invest:gated by gas-phase electron diffraction at 86” C Two du%inci conformers vrert identified, a more stable plenar Form with the furen oxygen and the czrbonyl oxygen syn and a less stable planar (or nearly p1ene.r) anti form_ Avummg that --he ho fcrms differ m their geometies ocly in fie O=C--C-O rorslon angles and vsurning the furan ring to bale Czv symmetry, the results for some of the d&Lances (ra) and angles (F,) are: r(C-I-I) = 1.110(20) X, r(C=O) - 1 ZOi(6) x, r(C-0) = 1378(10) L, r(C-cot X, tr(C-C)) (average i’ = 1,465(X3) cerbon--carbon distance in the furen r.ng) = 1 392(S) X dr(C-C) (difference befnveen single and double carbon--carbon distances m the furan nng) = 0.069 X (assumed), r(CC1) = 178’i(6) X, LC=C-COCI = 131 6(S)“, rC=CI-G = 110 S(4)", r-C=C-H = 127 7(13.4)“, .L~C=O = 125 S(8)” 2nd LC+C’-C~ = 111 S(6)” At 359 K the observed amount of the conformer wi+ch tne oxygen a&cornssyn was 69 8(14 2)E INTRODUCTION
Most conjugated acid chlorides such es 2propenoyl chlonde [l] , tram-Zbutenoyl chlorrde [2] and fumaryl chlorrde 131 are fo-und to exist rn d-12 gas phase as rmxtures of ro+tatronal isomers. One exception is 3-methyl-2-butinoyl chlonde whrch is reported as havrng oniy one form 2-Furoy: chlorrde (Fig. I) IS another mo’lecule of the sane type in which rotational isomerrsm might be possrble. The structure of the correspondmg aldehyde, 2-furaldehyde, has been extensively studred 14-133 and the results show that in the Iiauid and gas states two conformers with either syn or anti oxygen atoms coexist Less work has been reported on 2furoyl chloride; two spectroscopic studies 114, 151 indicate the presence of both syn and anti conformers and theoretical -X0caiculations El61 have given an energy difference between the conformers of 3 0 kcal mol-‘, the form with the oxygen aAtoms mtr having the lowest energy. Gas phase eiecxon tifiactlon gives, m addnion to bond distances and valence angles, mformatron ahout 30th tYne amount and type of conformers prewnt, and we report here the results of such an investrgatron
0022-2860/85/SO3.80
0 1985
Elsevier
Science
Publishers
B V.
256
Fig
1 Diagram
EXPEEIMENTAL
oi cotion?lers of 2-Euroyl chlorde. AND
DATA
REDUCTION
2-F-uroyl c_hloride (>98%) was obtamed from Fluka AG The sample purity was checked by GC before use. IX!fraction photographs were made on Kodak Electron Irnzge plates in thtl R-hers Eldlgraph KDG-2 117, I.83 at theuniversrty ofGs10, with a nozzletip temperature of 359 K. Three plates horn the long (50.012 cm) and srx frc n the short (25.012 cm) nozzle-to-plate distances were selected for an lysis. Tne electron wavelength was c&bra&d agmst benzene [19]. The prr cedures for obtammg the to’tel scattered mtenslty drstrrbution (@I,(s)> ant the molecular mt=znslty (d,(s)) have been described pre-xtoudy [20-221. Data from the long and short camera distances were obtained over the ranges 2 00 < s < 15.00 and 5 00 < s < 28.50 A-‘, respectively, 2~ mtervals As = 0.25 A4. The avenge experimental intensity curves are shown m Fig. 2, the Ir_drvrdual cumes end backgrounds ere avarIable as supplementary maternal [23]_ Electron scattering ampLi%udes and &as-e shrfts were calculated using Hartree-Fock potenti& [ 24, 1 for C, 0 uld CL, while molecular bonded potentials were used for H [25] STRUCTURE
ANALYSIS
An experimental rad~A distribution (RD) curve (Fig 3) was c&A.ated in c the function IA(s) = Sr,(s) the usual way by the Fourier transformation oA Z,Z,A~'A~ - exp (-Bs*) with 3 = 0.0025 A= Theoretical RD-curves were c&culated for conformers with the two oxygen atoms syn (a = 0” ) or czrrZr (a = 180” ) to each other, usmg reasonable values for bond distances and valence mgies. The torsion sensrtive drstmces are aLLlarger th-a 2.8 _A, and the outer part of the experimental RIB-curve is shown in P:g. 4 ‘together v&h theoretical curves for tie two conformers From these curves it was obvious that the major conformer was that vt-&&the oxygen at~~m!~S-JW However, the two theoretrcal curves ere not very d3fferent and some of the ant1 form m2y also be present Refinements of tie structure were czrrred out Ly the least-squares method [26l based on mtensrty curves by adjustmg one t~eoretr~4 curve to the *O average experL.menti curves (one each from the long 2nd short camera dir+ tances) using a urn6 wei@lt matrix. _Assuming the two conformers to have
357
I
I
0
I 4
1’ .;
5
:5
Fig. 2 Intens~ky cu_‘~es, d,(s) fo, rhr two camera dlsmces. in Table 1 Differeccc cnrve
b-------..
0
1
.
‘..
“’
%A-1
’ 30
Experlnental curves (Ex 1, Ek 2) are avs- ages of ali p!azs Theoretical curve (Th ) TX ~Aulated Go n CL= parmebrs (Di 1, Di 2) are Xx.-Th
‘1.
:
i5
&I
‘1
5
.
.
I
i
R,A
/i
Fig 3. Radnl distzbution cu~yes The experimental curve (Es.) IS calculated from the composite of the experizenti cum* of Fig 2 af+zr multlphcation by Z&~_,JA&a with E damgmg coefficient B = 0.0025 X’ and ~lth theoretical claka for 3 < s < 2.00 A-’ Ti;e tieorekzal curve (Th ) corresponds to the model of Tab!e 1 T3e di’ference curve (DC) 1s experimental minus theoretical.
radial distr!butio3 tunes for the conformers ir-ith the oxygen atoms FE 4 Theoretxal syn or anti together with the experimental curve Only the confoxmationally important parts of the curves are shown
equal geometry apart from the O-C-C=0 torsion angle Q, and assummg ‘he furan r-mg to have CZr-symmetry, the structure of 2-furoyl chloride can be described by 13 gecmetrrcal parameters, in our refinements taken as- r(C-H), r(C=O), (r(C-C)) = 0_5(r(C,=C,) r(C2-&)), L.r(C-C) = r(Cz-C3) r(C1=Cz), r(C -0). r(C,--C,), r(C-C!), LC,-CI=C, ILc2=ci*, LC=C-H. LC-C=O, LC-C-Cl and 0, the O=C-C-O torsion angle. Calculations of v,brationA amplitildes (1), perpendicular amphtr;dc corrections (K) and cenm*Jgti distortion constants (0) were carried out using a valence force field which was combmed from valence force fields of furan [27] and propenoyl chloride [27] _ In the least-squares refinements the vibrational amplitudes were kept constant at the calculated values. For the carbon-carbon bon& in the furan ring an accurate value for the average bond length could be de-ermined. However. the difference between r(C-C) and r(C=C) was tificuito determine due to overlapping peaks m the RD-curve In the tial refi-lemanz; this difference was therefore kept constant at the value (0.069 A) observed in a microwave spectroscopy invesfigation of the furan molecule [28]_ Tests showed that ‘Se U-C-C=0 torsion angle m the form v&h the oxygen a’toms syn, & 1, had z-o be close to O”, and in the final refinement it was assumed to have this value. In this final refmement srx distance parameters, six angle parameters and the conformational comPostion were refined sunultaneously. The fin& reslults are grven ti Table 1
259 TASLE Final
1 parameter
Parameter i( C-E) r(C=O)
r(C-0)
tic,-&)
v&es
for the structure
rafkI l.ilO(20) 1 207(6) 1 378(10) 1 465(X!) i.392(8)
LC=C-H LC-c=o L C-C-CI @Id GtC % syn
(0 C] 153.2111.6) 69.5(14.2)
c,=c,-c,
,Lc=c-0
0.076 0 039 0 046 0 04s
[0.069] l-787(6) 131 S(9) 110 9(4) 127 7(13 4) 125 818) 111 8(6)
L
&I,
0 051
Selected dependent angles and distances L c, =c,-C, 106 3(3] :c-O-c 105 6(6J L WC-c 117.1(B) Lc=C-Cl 122 5(i) r(C=C) 1357(8) 0 043 r(C,-C,) 1426(8) 0 048 ‘(C, - C5) 2 225(a) 0 952 r(C; - C, 1 2 569(11) 0 064 r(C: - 0,) 2.257(7) 0 050 r(C, - 0,) 2.427<13) 0 c71 r(C, - c, 1 2 183(10) 0 052
of 2-furnyl
chkwulea
Parameter
r( c, - o-) r(C_ - Cl)
r(C, - c, 1 tic, *C,! r(O_- cl) r(c, - Cl) r( c; - Cl’1
7
‘(C; - Cl) q 0, - Cl) r(C: - 0,)
r(C, - G-) tic,- “-) 40-O) r(Y, - Cl)
b OOsyn
r(H,
- Cl) r(H, - ClJ
r(C= ‘(C, r(C, r(0, r(C, r!C, r(C,
- Cl) - Cl) - Cl) -Cl) * O_) - o-) 0,)
J
00 CmCz
1s 0-L Cl) ) r(H, - Cl) I r(H, - Cl>) rl0
0)
2 362(11) 2 695(12) 3.670(10) 3 559(9) 2 620(9) S.OSO(lSj 4 487\16) 4.844(13) 3 9Sl(ll) 3 633(1-g) 4 V6(12) A 124j12) 2 603(16) 2 851(254) 5.323( 104) 5 913(41) 3.985(25 J -l 760(15] 4 196(33) 2 869(76) 3 OS9(211 4.367(14) 4_51S(!S) 3 500(2i)
0 CSi
4_WS(153) 5.843(21) 4 907(143)
0 134 0 123 0.164
0 076 0.060 0 064 0 C65 0.127 0.120 0 059 0 077 0.065 0 076 0 10’ 0 109 0 212 0 165 0 113 0 076 0.101 0.133 0 133 0 102 0.091 0 GiO 0 069
r aD:stacces (r,) and v:brawonaJ LTplltudes (1) are L-I Angs~-roms, mgis 1~ degrees. Parenthcsrzed uncertainties are 2r ana include estimates of systsmat:c errors and corre!akion m the experimental data. Quantitres m square brackets were kept cons-ant in the final refmement. b(r(C-C), = 0_5[r(C,=C,) I r(C,-C,)] ‘ar(C-C) = r(Cz-C1) - r(CI=C_)d*l is the O=*C-0 torsion angle of the conformer where the two oxygen atoms are syn &toeach other e+z is the O=C-C-C torsion angle in the anti conformer
and theoretical intensity and RD-curves cakulazd shown in Figs 2 and 3 toget!~r with difference matnx is gwen in Table 2.
from cures.
these results are The ccrrel2tion
DIsCLLsSION
Our investigation of gas phase Z-furoyl chlonde shows that the conformer rxtith the C=O and C=C double bonds antr to each other (oxygen atoms ~yrr) are the most stable. The same was also observed for 2-propenoy: chlcrlde
260
TABLE
2
Correlation
1 WC-c)) 2 r(c--01 3 rcc-H) 4 r(C,-q) 5r(C=O) 6 r
UStandard
matrix
x 100
0-a
71
0.0019 00023 00049 00031 0.0014 0.0013 029 0.15 4.45 0.27 0.20 3.86 a 74
iO0
deviatmn
for the r1 -S 100
ptrame&ersof 2-furoyl ‘3
r4
rs
=6
-24 21 100
1 -3 -13 100
2 13 a -41 100
-8 9 10 -35 6 1oJ
from leastsquares
refinem
chloride L-
-42 45 15 -31 15 26 100
4 -12
4
L,, 4
3-4 -7 24 57 4 -29 4 -30 6 46 -1 100 23 100
LII
3 -7 2 2 11 -10 -35 -1 21 7 53-m 49 -1 -30 3 28 -27 1co -60 1CO
4,
‘5.3,”
23 28 -23 -8 11 24 -30 -23 8 0 4 3 10 -31 -10 15 46 17 49 -2 -37 -12 100 0 100
mts
[l] . Our results are the-&ore in disagreement with the theoretrcal JMO-calculations [16] E we assume the two conformers of 2-furoyl chloride to have approxrmately the same entiopy, the observed conformational composition corresponds to an energy difference of about 6 6 kcai mol-‘_ This is slightly higher than the value observed ;O 3 -t 0.4 kcal mol-‘) for propenoyl chloride ]I] In 2-furaldehyde the csnformer with the oxygen atolms s;zti (G=C and C=O syn) was observed to be the most abundant form in the gas phase wi’& 69(g)% present at 323 K 141, correspondmg to an energy difference of -0.5 = 0.4 kcal mol-’ between 00 s3n and 00 cntr. Therefore, while 2-furoyl chloride and propenoyl chloride have smular conformational properties, 2-furaldehyde and propenal are very drfferent since propenal m the gas phase exists predomirzntly as a conformer with C=C and C=O anti [29, 303. It would appear thet m attraction exists m 2-fureldehyde between the furan oxygen and the aldehyde hydrogen, which stabilizes the conformer wn91 C=C and C=O vn. In Table 1 we have reported a torsion angle of 153(12)” for the high-energy form of 2-furoyl chlorde. This was the result obtained when a torsronahy stiff model was used for this conformer. However, our data arc also consistent with a planar conformer undergoing large torsionai motion or WIG-I a mode! havmg a low torsional barer at the planar no&ion The electron dl!fraction experiment cannot distinguish between these possibilities. In a possrble pianar form of this Qpe, the distance between the chlorine and the furan oxygen will be very short, and it is therefore not unlikely that a small hump exLct.s m the torsional potential function at & = lE!O” _ In Table 3 the geometrical parameters of 2-furoyl chloride are compared with those for some related molecilles. The geometry of the furan Lug is not much changed by the presence of the COCl group_ Valence ares and bond distances are ve_ry simrlar in furan and 2-furoyl chloride, and 2-furaldehyde
261
TABLE
3
Geometry
of furoyl
chloride
P-Furoyl
and
some
chloride
relntid
moleculesa
2-Fur-zldehyde
Furz n
P -openoyl
LC, =c,-c, Lc,=c,--o
i-207(6) 1.787(6) i 465(13) 1357(B) 1 42618) 1.378(101 131 6(9) 125 E(8) 106.3(3) 110 9(4)
1.453[71 [l-361] [ 1- 4311 [1362] 131 7(d) 122.7(S) Cl06 I] [i10.7]
106 07(2) 110 65(2)
LC-O-C
105
[lo6
106_56(
l-(C=O)
tic--c11 4c-G 1 r(C=c)
tic,--c, 1 tic--o) Lcl=c,-c, LC-c-o
Dls+ace Ref
types
8(8)
ra This work
=Dlstances in _4ngstroms, meanrngs in the ddFerent
1.192(2) I78S(j1 1.484(4) 1339(2)
1_212(4)
ra 4
51
chloride
1 3610(3) i 4301(5) l-3622(2)
123.4(7) 125 2(Z)
rs
38
2) 7a 1
angles in degrees Parenthesized tir cartamtiea may have different investigations. Quantxties in squarc~ bra&s& were -Gumed
and 2-furoyl chloride also have similar geometries. LC--C=O is larger in 2-furoyl chloride, but thk is often obserr;el for ac_d chiondes relative to the aldehydes. From Tab!e 3 11; can also be seen that the C=O ad C=C double bonds are longer and the C-C smgle bond is shon;e - in 2-furoyl chloride than ti propenoyl chloride, mdlcating that conjugation is more important m 2-fiiroyl chloride. ACKNOWLEDGZMENTS
We are grateful to Slv.mg. R Selp for help in recordmg *he electroE diffraction data and to Ms. S. Gundersen for +te&nkal ass;stance. Fmax~cxzl support from the Norwegm Research Council fo1 Science and the Humanities is gratefully acknowledged REFERENCES 1 2 3 4 5 6 7 8 9
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262
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