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Infrared spectrum and structure of some derivatives of formhydroxamic acid
JOURNAL
OF
MOLECULAR
infrared
SPECTROSCOPY
Spectrum
and
3, 73-77
Structure
(1959)
of Some
Formhydroxamic Part II. Methyl
Derivatives
of
Acid
Formyl Chloride
Oxime
A. E. PARSONS* Edward Davies
Chemical Laboratories,
University
College of Wales, Aberystwyth,
Wales
The spectrum from 6504000 cm-l of methyl formyl chloride oxime has been studied in the gaseous and liquid states. The molecule has a structure corresponding to the enolic form of O-methyl formhydroxamic acid, (i.e., to the enolic form of N-methoxyformamide). A study of the band contours of the vapor phase absorptions indicates a planar configuration of the H. C(C1) :NOC grouping with a trans disposition of the CHS group with respect to the Cl atom. The frequencies of the (-NOCH,) group vibrations simulate closely those in O-methyl formhydroxamic acid but significant differences in the (C-N) and (CH) frequencies are noted.
1
Methyl formyl chloride oxime is the chloro derivative of the enolic form of O-methyl formhydroxamic acid. The coplanarity of the H. C(C1) :NO group is assured since the C and N atoms are approximately sp’ hybridized. As in O-methyl formhydroxamic acid (1) there is some uncertainty as to the precise location of the CH, group and the two extreme configurations are represented by models I and II.
I
CHs I
II
The band contours of the vapor phase absorptions allow a discrimination of these configurations. * Present address: 4, California.
Department
of Mineral
Technology, 73
University
of California,
Berkeley
74
PARSOTiS
The observed ,(C=S) and y(CCl) frequencies differ from the normal values quoted by Bellamy (2) and this is explained in terms of molecular orbital theory. The pronounced change in the CH vibrational frequencies as compared wit,h O-methyl formhydroxamic acid can be attributed in part to the absence of interaction between 6(CH) and the amide group vibrations. EXPERIMENTAL
The compound was prepared according to the met’hod (3) and had a boiling point 68°C. The vapor pressure sufficiently high to allow the spectrum to be recorded cell. The spectrum of the liquid was obtained by using halite plates. TABLE
recommended by Biddle at room temperature is in an 8-cm path length a capillary film between
I
FREQUENCY ASSIGNMENT IN METHYL FORMYI, CHLORIDE OXIME (FREQUENCIES IN CM-‘) Liquid
Assignment
Vapa1
3083 (3 )
3093 (fS)
v(CH)
2976 (2)
2993 (IS)
2v(CCl)
2941(4) 2904 (2)
2954 (3) 2887 (I$)
26, (CH,) Pv,(NOC)
2825 (2) 1961(O) 1835(O) 1806(l)
2830(l)
2UCH.d v,(NOC) ..(NOC) Sv,(NOC)
1597 (6)
1613 (3) \1572
1555(3) 1466(3) 1443 (3) 1274 (4) 1190(2) 1156(l) 1063 (8)
905 (9) 806 (2)
(2) ‘i 1563 14640) 1276(2) 1182(l) 1155(l) [ 1084 1 1080 (8) 1072 917 911(8) 905 813(?i) I 802
784(9)
(5) 789
+
&(C&) +
r(CC1)
+ v,(NOC) + u(CCI)
v(CN) B”(CC1) &(CHd &(CHa) s(CH) r(CH,) out-of-plane r(CH,) in-plane Y, (NOC)
V,(NOC) S(CN0) v(CCI)
IR SPECTRUM
OF METHYL
RESULTS
AND
FORMYL
CHLORIDE
75
OXIME
DISCUSSION
Table I summarizes the absorptions observed and the assignment proposed. The spectrum of the vapor phase is shown diagrammatically in Fig. 1. The Y,(NOC) and Y~(~TOC)vibrations have strong absorption centers in the vapor phase spectrum at 1080 cm-’ and 911 cm-‘, respectively. These contours have well defined P and R branches at CCL 6 cm-’ from the central Q branch. In configuration I these vibrations will have hybrid A.B. character and the calculated P-Q separation [from Badger and Zumwalt’s relations (41 is ca 7 cm-‘. The observed contours and their component separations are in close agreement with those calculated for model I but bear no relation to those calculated for model II. li’urthermore, it is almost impossible to construct a Courtauld’s model for II. The Y,(NOC) and YJXOC) show little or no C character and free rotation
0‘ 3200
I
3100
3ow
2700
2900
T
’ lool
I
3
2 iiJ 100 I
0
1
LJL‘i;,
I200
II00
FIG. 1. Infrared spectrum 3200-2700 cm-l and 1700-700
of methyl cm-l.
IO00
900
formyl chloride
800
700
oxime vapor at 20°C in the regions
76
PARSONS
about the N-O bond or an out-of-plane configuration of the CHa group is thus precluded. On t’his basis the molecule is assigned the configuration I. The v(C=N) is assigned to the ill-defined absorption at 1613 cm-’ in the vapor and to the strong absorption at 1597 cm-’ in the liquid. Since the amide group is absent in this derivative a normal Y(C=N) frequency is expect,ed. Bellamy (2) quotes the region 1690-1640 cm-’ for this vibration. In acetonoxime (5) in the vapor it appears at 1662 cm-‘. The lower frequency value in methyl formyl chloride oxime results principally from the delocnlization of the a-electrons of the C-N bond into the 2pl atomic orbital of the chlorine atom. The (C-Cl) bond thus acquires some double bond charact,er at the expense of the (C=N) bond. In chloroethylene a similar type of interaction occurs and the C-Cl bond is considered to have about 5 percent double bond character (6). The increased (C-Cl) bond order in methyl formyl chloride oxime accounts for the relatively high frequency observed for the (C-Cl) vibration : this vibration absorbs strongly at 784 cm-’ (liquid) and ca 795 cm-’ (vapor), see 732 cm-’ in CH,CI. The frequencies of the vibrations in the -NOCHs group simulate closely the corresponding frequencies in O-methyl formhydroxamic acid; t,his implies t.hnt the structure of this group is repeated, with the (N-O) links having predominantly single bond character. In contrast there is a considerable divergence in the frequencies for the (CH) vibrational modes. A comparison of (CH) group frequencies (given in Table II in cm-‘) in methyl formyl chloride oxime (M.F.C.O.) and O-methyl formhydroxamic acid (O.M.F.A.) serves to indicate the changes in bonding in these molecules. It is clear that in methyl formyl chloride oxime the (C-H) bond is appreciably stronger than in O-methyl formhydroxamic acid. These changes are of the same type as those for the (C-H) bond in going from methane through ethylene to acetylene and they can be described in the following molecular orbital terms. The a,toms attached to the central C atom in the two molecules are dissimilar and the C hybrid atomic orbitals are nonequivalent. The stronger (C-H) bond in methyl formyl chloride oxime indicates excess s character in the C-atom hybrid orbital forming this bond, relative to the corresponding bond orbital in O-methyl formhydroxamic acid. For the C-atom hybrid orbitals to be orthogonal the remaining TABLE COMPARISON
OF (CH) GROUP
II
FREQUENCIES
IN M.F.C.O.
Liquid
Vapor
Liquid
O.M.F.A. Vapor
3083 1274
3093 1276 1025?
2899 1375 1026
2895 1366 1033
M.F.C.O.
v(CH) a(CH) Y (CH)
AND 0.M.F.A
IR
SPECTRUM
OF METHYL
FORMYL
CHLORIDE
77
OXIME
two hybrid orbit& in methyl formyl chloride oxime must possess p character in excess of the corresponding ones in O-methyl formhydroxamic acid. The change in the 6(CH) frequency may also be partly due to the absence of interaction which probably occurs in O-methyl formhydroxamic acid between the above vibration and vibrations in the amide group. CONCLUSION
The evidence from the spectrum seems to be consistent with that anticipated for structure I. Consonant with this is the absence of the characteristic amide frequencies: the present molecule is one of the few amide derivatives corresponding to the hydroxy-imino configuration. The molecule has features in common with O-methyl formhydroxamic acid, principally in the (NOCH3) group. The Y(C-N) and v(C-Cl) frequencies indicated that there is some delocalization in the NCCl group. The absence of the amide group has a noted effect in the (C-H) vibrational frequencies: whereas the duplication of the NOCH3 group frequencies serves to show that the vibrations in this group are independent of the amide group vibrations. ACKNOWLEDGMENTS The author wishes to express his gratitude to Dr. Manse1 Davies and to Dr. W. J. OrvilleThomas for much helpful advice and discussion. He also wishes to thank the Department of Scientific and Industrial Research for a Maintenance Award. RECEIVED:
June 20, 1958 REFERENCES
1. 2. 9. $. 6. 6’.
Mol. Spectroscopy 2, 566-574 (1958). J. BELLAMY, “Infra-Red Spectra of Complex Molecules.” Methuen, C. BIDDLE, A. C. J. Remsen 33, 60 (1905). M. BADGER, AND L. R. ZUMWALT, J. Chem. Phys. 6, 711 (1938). CALIFANO, AND W. LUTTKE,~. Physik. Chem. 6, 83 (1956). B. WILSON, Disc. Faraday Sot. 9, 108 (1950).
A. E. PARSONS, J.
L. H. R.
S. E.
London,
1954.
OF
MOLECULAR
infrared
SPECTROSCOPY
Spectrum
and
3, 73-77
Structure
(1959)
of Some
Formhydroxamic Part II. Methyl
Derivatives
of
Acid
Formyl Chloride
Oxime
A. E. PARSONS* Edward Davies
Chemical Laboratories,
University
College of Wales, Aberystwyth,
Wales
The spectrum from 6504000 cm-l of methyl formyl chloride oxime has been studied in the gaseous and liquid states. The molecule has a structure corresponding to the enolic form of O-methyl formhydroxamic acid, (i.e., to the enolic form of N-methoxyformamide). A study of the band contours of the vapor phase absorptions indicates a planar configuration of the H. C(C1) :NOC grouping with a trans disposition of the CHS group with respect to the Cl atom. The frequencies of the (-NOCH,) group vibrations simulate closely those in O-methyl formhydroxamic acid but significant differences in the (C-N) and (CH) frequencies are noted.
1
Methyl formyl chloride oxime is the chloro derivative of the enolic form of O-methyl formhydroxamic acid. The coplanarity of the H. C(C1) :NO group is assured since the C and N atoms are approximately sp’ hybridized. As in O-methyl formhydroxamic acid (1) there is some uncertainty as to the precise location of the CH, group and the two extreme configurations are represented by models I and II.
I
CHs I
II
The band contours of the vapor phase absorptions allow a discrimination of these configurations. * Present address: 4, California.
Department
of Mineral
Technology, 73
University
of California,
Berkeley
74
PARSOTiS
The observed ,(C=S) and y(CCl) frequencies differ from the normal values quoted by Bellamy (2) and this is explained in terms of molecular orbital theory. The pronounced change in the CH vibrational frequencies as compared wit,h O-methyl formhydroxamic acid can be attributed in part to the absence of interaction between 6(CH) and the amide group vibrations. EXPERIMENTAL
The compound was prepared according to the met’hod (3) and had a boiling point 68°C. The vapor pressure sufficiently high to allow the spectrum to be recorded cell. The spectrum of the liquid was obtained by using halite plates. TABLE
recommended by Biddle at room temperature is in an 8-cm path length a capillary film between
I
FREQUENCY ASSIGNMENT IN METHYL FORMYI, CHLORIDE OXIME (FREQUENCIES IN CM-‘) Liquid
Assignment
Vapa1
3083 (3 )
3093 (fS)
v(CH)
2976 (2)
2993 (IS)
2v(CCl)
2941(4) 2904 (2)
2954 (3) 2887 (I$)
26, (CH,) Pv,(NOC)
2825 (2) 1961(O) 1835(O) 1806(l)
2830(l)
2UCH.d v,(NOC) ..(NOC) Sv,(NOC)
1597 (6)
1613 (3) \1572
1555(3) 1466(3) 1443 (3) 1274 (4) 1190(2) 1156(l) 1063 (8)
905 (9) 806 (2)
(2) ‘i 1563 14640) 1276(2) 1182(l) 1155(l) [ 1084 1 1080 (8) 1072 917 911(8) 905 813(?i) I 802
784(9)
(5) 789
+
&(C&) +
r(CC1)
+ v,(NOC) + u(CCI)
v(CN) B”(CC1) &(CHd &(CHa) s(CH) r(CH,) out-of-plane r(CH,) in-plane Y, (NOC)
V,(NOC) S(CN0) v(CCI)
IR SPECTRUM
OF METHYL
RESULTS
AND
FORMYL
CHLORIDE
75
OXIME
DISCUSSION
Table I summarizes the absorptions observed and the assignment proposed. The spectrum of the vapor phase is shown diagrammatically in Fig. 1. The Y,(NOC) and Y~(~TOC)vibrations have strong absorption centers in the vapor phase spectrum at 1080 cm-’ and 911 cm-‘, respectively. These contours have well defined P and R branches at CCL 6 cm-’ from the central Q branch. In configuration I these vibrations will have hybrid A.B. character and the calculated P-Q separation [from Badger and Zumwalt’s relations (41 is ca 7 cm-‘. The observed contours and their component separations are in close agreement with those calculated for model I but bear no relation to those calculated for model II. li’urthermore, it is almost impossible to construct a Courtauld’s model for II. The Y,(NOC) and YJXOC) show little or no C character and free rotation
0‘ 3200
I
3100
3ow
2700
2900
T
’ lool
I
3
2 iiJ 100 I
0
1
LJL‘i;,
I200
II00
FIG. 1. Infrared spectrum 3200-2700 cm-l and 1700-700
of methyl cm-l.
IO00
900
formyl chloride
800
700
oxime vapor at 20°C in the regions
76
PARSONS
about the N-O bond or an out-of-plane configuration of the CHa group is thus precluded. On t’his basis the molecule is assigned the configuration I. The v(C=N) is assigned to the ill-defined absorption at 1613 cm-’ in the vapor and to the strong absorption at 1597 cm-’ in the liquid. Since the amide group is absent in this derivative a normal Y(C=N) frequency is expect,ed. Bellamy (2) quotes the region 1690-1640 cm-’ for this vibration. In acetonoxime (5) in the vapor it appears at 1662 cm-‘. The lower frequency value in methyl formyl chloride oxime results principally from the delocnlization of the a-electrons of the C-N bond into the 2pl atomic orbital of the chlorine atom. The (C-Cl) bond thus acquires some double bond charact,er at the expense of the (C=N) bond. In chloroethylene a similar type of interaction occurs and the C-Cl bond is considered to have about 5 percent double bond character (6). The increased (C-Cl) bond order in methyl formyl chloride oxime accounts for the relatively high frequency observed for the (C-Cl) vibration : this vibration absorbs strongly at 784 cm-’ (liquid) and ca 795 cm-’ (vapor), see 732 cm-’ in CH,CI. The frequencies of the vibrations in the -NOCHs group simulate closely the corresponding frequencies in O-methyl formhydroxamic acid; t,his implies t.hnt the structure of this group is repeated, with the (N-O) links having predominantly single bond character. In contrast there is a considerable divergence in the frequencies for the (CH) vibrational modes. A comparison of (CH) group frequencies (given in Table II in cm-‘) in methyl formyl chloride oxime (M.F.C.O.) and O-methyl formhydroxamic acid (O.M.F.A.) serves to indicate the changes in bonding in these molecules. It is clear that in methyl formyl chloride oxime the (C-H) bond is appreciably stronger than in O-methyl formhydroxamic acid. These changes are of the same type as those for the (C-H) bond in going from methane through ethylene to acetylene and they can be described in the following molecular orbital terms. The a,toms attached to the central C atom in the two molecules are dissimilar and the C hybrid atomic orbitals are nonequivalent. The stronger (C-H) bond in methyl formyl chloride oxime indicates excess s character in the C-atom hybrid orbital forming this bond, relative to the corresponding bond orbital in O-methyl formhydroxamic acid. For the C-atom hybrid orbitals to be orthogonal the remaining TABLE COMPARISON
OF (CH) GROUP
II
FREQUENCIES
IN M.F.C.O.
Liquid
Vapor
Liquid
O.M.F.A. Vapor
3083 1274
3093 1276 1025?
2899 1375 1026
2895 1366 1033
M.F.C.O.
v(CH) a(CH) Y (CH)
AND 0.M.F.A
IR
SPECTRUM
OF METHYL
FORMYL
CHLORIDE
77
OXIME
two hybrid orbit& in methyl formyl chloride oxime must possess p character in excess of the corresponding ones in O-methyl formhydroxamic acid. The change in the 6(CH) frequency may also be partly due to the absence of interaction which probably occurs in O-methyl formhydroxamic acid between the above vibration and vibrations in the amide group. CONCLUSION
The evidence from the spectrum seems to be consistent with that anticipated for structure I. Consonant with this is the absence of the characteristic amide frequencies: the present molecule is one of the few amide derivatives corresponding to the hydroxy-imino configuration. The molecule has features in common with O-methyl formhydroxamic acid, principally in the (NOCH3) group. The Y(C-N) and v(C-Cl) frequencies indicated that there is some delocalization in the NCCl group. The absence of the amide group has a noted effect in the (C-H) vibrational frequencies: whereas the duplication of the NOCH3 group frequencies serves to show that the vibrations in this group are independent of the amide group vibrations. ACKNOWLEDGMENTS The author wishes to express his gratitude to Dr. Manse1 Davies and to Dr. W. J. OrvilleThomas for much helpful advice and discussion. He also wishes to thank the Department of Scientific and Industrial Research for a Maintenance Award. RECEIVED:
June 20, 1958 REFERENCES
1. 2. 9. $. 6. 6’.
Mol. Spectroscopy 2, 566-574 (1958). J. BELLAMY, “Infra-Red Spectra of Complex Molecules.” Methuen, C. BIDDLE, A. C. J. Remsen 33, 60 (1905). M. BADGER, AND L. R. ZUMWALT, J. Chem. Phys. 6, 711 (1938). CALIFANO, AND W. LUTTKE,~. Physik. Chem. 6, 83 (1956). B. WILSON, Disc. Faraday Sot. 9, 108 (1950).
A. E. PARSONS, J.
L. H. R.
S. E.
London,
1954.