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Proton chemical shift-charge density correlations in substituted alkyl derivatives.
TetrahedronLettersNo.55, pp. 5025-5028,1969. PergamonPress. Printed in Great Britain.
PRCTCN CHEXICAL SBIFT-CHARGRDENSITY CORRBLATICNSIN SUSSTITD'IRD ALIYL DERIVATIVES. P. Lazscrettiand
F.
Taddei
Istitutedi Chiaica Clrganica, Via Campi 183, 41100 Modena (Italy). (Received in IK 2 May 1969; accepted for publication 27 June 1969)
Attempts have been made in recent years to correlateproton chemical shifts and charge densitiesin differentseries of compounds.'Mono substitutedmethanes and ethanes,ouing to their relativelysimple electronicstructure,seem to yield more useful informationon the electronicmechanism involved in determiningthe proton chemical shift.2,3,4.5,6In these capounds 13 correlationsbetueenC and H' chemical shifts and substituentelectronegativity vere observed,2-5 although several limitationsvere found to be present. It is caronly accepted that beside electroDl density changes around the proton dme to the electronegativity of substitumts, other 7 3,4 factors,namely magnetic anisotropy and electrostaticfield effects, are important.Recently6 13 it has been observed that good correlationsbetween C and 'H chemical shifts and substituent electronegativity for methyl and ethyl derivativescan be Pout&d,if correctionsto the experimentalshifts are alloued for lone pair dipole manents in substituentgroups. We present now a series of correlationsinvolvingproton chemical shifts for mono and polysubstitutedaliphatichydrocarti derivativesand positivecharge densities(111 hydrogen determined by a MC-LCAO method proposedby Del Re.8 The method provides charge densitiesvicb are consistentwith the dipole moments of the moleculesexamined and they scan to have the properties 8.9 required by real charges. The compoundsexaminedhere, the relativeproton chemical shifts and proton charge densities are listed in the Table. Charge densities(qh) for several compoundsvere colputedby means Of 8
the parametersgiven by Del Be. In other cases we have evaluated the X0-LCAO parametersby employingknown values of dipole moments: the parametersobtaineduere made consistentwith those of other substituentsbelongingto the same row or group of
the
periodic SyStcll.
The
plot
of the chemical shifts in 5 units against qR, reported in the Figure, clearly shows that a linear relationshipexists for substitutedaliphaticcompoundslimited to substituentsOf the same row of the periodic system. This holds for mono-
and polysubstituted methanes and branched
aliphaticderivatives.This fact should lead to the conclusionthat, in substitutedaliphatic compounds,the protcn chanical shift is mainly determinedby the electroniccharge On the hydrogenatom. Neverthelessan explanationshould be found for the fact that charge densities
3025
No.35
3026 TABLE *
nr
6’
Corpound
Compound
1
(CH ) N 33
2,ll
0,041
19
CH22 F
5.62 b
0,075
2
(CH3)20
3.17
0,053
20
CJ3CH2F
1.35
0,042
3
CH3CC1 3
2.64
0,051
21
+SRt)2
3,59
0,083
4
Gqo=)2
4.56
0,062
22
(CH3)2S
2100
0;064
5
E(oRt)3
5.03
0,069
23
G@Rt)3
4,83
0,101
2,34=
0,049
24
CH2Cl2
5.13
0,105
6
%3N"2
7
CJ$H2NH2
1,08=
0,040
25
CHCl3
7,oa
0,131
a
CqH2SH
I,laa
0,042
26
CH3C1
2,85
0,075
9
CH3CH20H
1,21=
0,041
27
%SH
2,09=
0,058
10
CH OH
3,37=
0,055
28
(CH3)4Si
0,oo
0,039
11
(cH_CH2)2S
1,11=
0,042
29
(CH_)3SiCH2C1 0,12b
0,043
4,26b
0,060
30
CH3Br
2,47
0,079
12
CB3F
13
(CH_)2CHC1
1,51
0,043
31
CH2Bt2
4.78
0,112
I4
(G!3CH2)20
1,14
0,040
32
CHBr3
6,72
0,142
15
(CH_)3CCl
1,59
0,042
33
(CH3)3As
o,40d
0,040
16
CH CH Cl -32
1,32
0,043
34
(CR3)4Ce
0,127d 0,042
l?
(G!q2~
2,31
0,047
35
CH3CH2Br
1,6a
0,044
la
CHF3
6*3ab
0,085
36
(CH3)3SiH
O,Oad
0,033
+
Where not specifiedchemical shifts were measured in our laboratory,by employing a Varian DP 60 spectrometeroperatingat 56.4 MC.
t in ppm from TMS (negativevalues). a
Ref. 2.
b
Ref. 10.
' Ref. 11.
d
Ref. 12.
3027
No.35
correlate differently with protcm cbaical
shifts whea substituents belong to different rows of
the periodic system. No doubt
in substituted aliphatic derivatives is a smoothly varying 5i function of the position of the substituent in the periodic table since it follows parallely the electrohegativity
of substituents as one goes across the periodic table aad the same holds
roughly for protou chemical shifts,
5.6
but evidently the two quantities do not possess the same
slope. The slopes of the linear correlations reported in the Figure should throw light on the
mechanism of tnansmission of substituent effects to the proton, and thismechani?lr seas
to be
the same within the same row of the periodic systan. Since elements of the same rov possess the same inner electron shell and elemental properties are mainly connected to the outer electron configuration,
these slopes could reflect such a situation; this consequently should also mean
that proton chemical shifts and charge densities have a different sensitivity to valence electI+On
configuration.
Further elaborationof the data is required to clear up this point. A preliainarycheck cm carbon charge densities (SC), evaluatedby the same method, seems to indicate that good fits 13 is vell related to JC13 chemical shifts, and the product q can be obtainedvith C C'PH -H ccsIp1ing constants. A complete descriptionof the results obtainedwill be reported soon.
WC vhish to aknovledgeMr. E. Mancini of the "Laboratorioper lo studio di compostide1 carbonio contenentieteroatomi",C.N.B., Bologna for technicalassistencein recording P.M.R. spectra.
REFERENCES
1)
T. Schaefer,V.G. Schneider,Can.J.Chem.,4l, 966 (1963); P.J. Black, R.D. Brown and H.L. Heffernan,Austr.J.Chem.,20, 1305, 1325 (1967);J.M. Sichel and M.A. Whitehead, Theor.Chim.Acta, 2, 35 (1966).
2)
B.P. Dailey and J.N. Shoolery,J.Am.Chem.Soc.,n, 3977 (1955).
3)
J.R. Cavanaugh and B.P. Dailey, J.Chem.Phys.,34, 1089 (1961).
4)
II,Spieseckeand W.G. Schneider,J.Chem.Phys.,3&
5)
F. Taddei, C. Zauli, contributionto "NuclearMagnetic Resonancein Chemistry" Ed. B. Pesce - Academic Press Inc. - Nev York - 1965 - p. 179.
6)
P. Bucci, J.Am.Chem.Soc.,PG, 252 (1968).
7)
T.W. Marshall and J.A. Pople, Mol.Phys.,1, 199 (1958).
8)
G. Del Be, J.Chem.Soc.,1958, 4031.
P)
G. Del Re, 8. Pullman and T. Yonezava,Biochim.andBiophysic.Acta,
IO)
W.
722 (1961).
2,
153
(1963).
l
Brugel, "NuclearMagnetic Resonancespectra and chemiaal structure"vol. I Academic Press - Nev York - London, 1967.
11) D.W. hathieson "Interpretationof organic spectra"- Academic Press Inc. - London, 1965. 12) H.L. Maddox, S.L. Staffordand H.D. Kaesz in "Advancesin organometallicchemistry" Edited by F.G.A. Stone and R. West - Academic Press - New York - London, 1965 - vol. 3.
PRCTCN CHEXICAL SBIFT-CHARGRDENSITY CORRBLATICNSIN SUSSTITD'IRD ALIYL DERIVATIVES. P. Lazscrettiand
F.
Taddei
Istitutedi Chiaica Clrganica, Via Campi 183, 41100 Modena (Italy). (Received in IK 2 May 1969; accepted for publication 27 June 1969)
Attempts have been made in recent years to correlateproton chemical shifts and charge densitiesin differentseries of compounds.'Mono substitutedmethanes and ethanes,ouing to their relativelysimple electronicstructure,seem to yield more useful informationon the electronicmechanism involved in determiningthe proton chemical shift.2,3,4.5,6In these capounds 13 correlationsbetueenC and H' chemical shifts and substituentelectronegativity vere observed,2-5 although several limitationsvere found to be present. It is caronly accepted that beside electroDl density changes around the proton dme to the electronegativity of substitumts, other 7 3,4 factors,namely magnetic anisotropy and electrostaticfield effects, are important.Recently6 13 it has been observed that good correlationsbetween C and 'H chemical shifts and substituent electronegativity for methyl and ethyl derivativescan be Pout&d,if correctionsto the experimentalshifts are alloued for lone pair dipole manents in substituentgroups. We present now a series of correlationsinvolvingproton chemical shifts for mono and polysubstitutedaliphatichydrocarti derivativesand positivecharge densities(111 hydrogen determined by a MC-LCAO method proposedby Del Re.8 The method provides charge densitiesvicb are consistentwith the dipole moments of the moleculesexamined and they scan to have the properties 8.9 required by real charges. The compoundsexaminedhere, the relativeproton chemical shifts and proton charge densities are listed in the Table. Charge densities(qh) for several compoundsvere colputedby means Of 8
the parametersgiven by Del Be. In other cases we have evaluated the X0-LCAO parametersby employingknown values of dipole moments: the parametersobtaineduere made consistentwith those of other substituentsbelongingto the same row or group of
the
periodic SyStcll.
The
plot
of the chemical shifts in 5 units against qR, reported in the Figure, clearly shows that a linear relationshipexists for substitutedaliphaticcompoundslimited to substituentsOf the same row of the periodic system. This holds for mono-
and polysubstituted methanes and branched
aliphaticderivatives.This fact should lead to the conclusionthat, in substitutedaliphatic compounds,the protcn chanical shift is mainly determinedby the electroniccharge On the hydrogenatom. Neverthelessan explanationshould be found for the fact that charge densities
3025
No.35
3026 TABLE *
nr
6’
Corpound
Compound
1
(CH ) N 33
2,ll
0,041
19
CH22 F
5.62 b
0,075
2
(CH3)20
3.17
0,053
20
CJ3CH2F
1.35
0,042
3
CH3CC1 3
2.64
0,051
21
+SRt)2
3,59
0,083
4
Gqo=)2
4.56
0,062
22
(CH3)2S
2100
0;064
5
E(oRt)3
5.03
0,069
23
G@Rt)3
4,83
0,101
2,34=
0,049
24
CH2Cl2
5.13
0,105
6
%3N"2
7
CJ$H2NH2
1,08=
0,040
25
CHCl3
7,oa
0,131
a
CqH2SH
I,laa
0,042
26
CH3C1
2,85
0,075
9
CH3CH20H
1,21=
0,041
27
%SH
2,09=
0,058
10
CH OH
3,37=
0,055
28
(CH3)4Si
0,oo
0,039
11
(cH_CH2)2S
1,11=
0,042
29
(CH_)3SiCH2C1 0,12b
0,043
4,26b
0,060
30
CH3Br
2,47
0,079
12
CB3F
13
(CH_)2CHC1
1,51
0,043
31
CH2Bt2
4.78
0,112
I4
(G!3CH2)20
1,14
0,040
32
CHBr3
6,72
0,142
15
(CH_)3CCl
1,59
0,042
33
(CH3)3As
o,40d
0,040
16
CH CH Cl -32
1,32
0,043
34
(CR3)4Ce
0,127d 0,042
l?
(G!q2~
2,31
0,047
35
CH3CH2Br
1,6a
0,044
la
CHF3
6*3ab
0,085
36
(CH3)3SiH
O,Oad
0,033
+
Where not specifiedchemical shifts were measured in our laboratory,by employing a Varian DP 60 spectrometeroperatingat 56.4 MC.
t in ppm from TMS (negativevalues). a
Ref. 2.
b
Ref. 10.
' Ref. 11.
d
Ref. 12.
3027
No.35
correlate differently with protcm cbaical
shifts whea substituents belong to different rows of
the periodic system. No doubt
in substituted aliphatic derivatives is a smoothly varying 5i function of the position of the substituent in the periodic table since it follows parallely the electrohegativity
of substituents as one goes across the periodic table aad the same holds
roughly for protou chemical shifts,
5.6
but evidently the two quantities do not possess the same
slope. The slopes of the linear correlations reported in the Figure should throw light on the
mechanism of tnansmission of substituent effects to the proton, and thismechani?lr seas
to be
the same within the same row of the periodic systan. Since elements of the same rov possess the same inner electron shell and elemental properties are mainly connected to the outer electron configuration,
these slopes could reflect such a situation; this consequently should also mean
that proton chemical shifts and charge densities have a different sensitivity to valence electI+On
configuration.
Further elaborationof the data is required to clear up this point. A preliainarycheck cm carbon charge densities (SC), evaluatedby the same method, seems to indicate that good fits 13 is vell related to JC13 chemical shifts, and the product q can be obtainedvith C C'PH -H ccsIp1ing constants. A complete descriptionof the results obtainedwill be reported soon.
WC vhish to aknovledgeMr. E. Mancini of the "Laboratorioper lo studio di compostide1 carbonio contenentieteroatomi",C.N.B., Bologna for technicalassistencein recording P.M.R. spectra.
REFERENCES
1)
T. Schaefer,V.G. Schneider,Can.J.Chem.,4l, 966 (1963); P.J. Black, R.D. Brown and H.L. Heffernan,Austr.J.Chem.,20, 1305, 1325 (1967);J.M. Sichel and M.A. Whitehead, Theor.Chim.Acta, 2, 35 (1966).
2)
B.P. Dailey and J.N. Shoolery,J.Am.Chem.Soc.,n, 3977 (1955).
3)
J.R. Cavanaugh and B.P. Dailey, J.Chem.Phys.,34, 1089 (1961).
4)
II,Spieseckeand W.G. Schneider,J.Chem.Phys.,3&
5)
F. Taddei, C. Zauli, contributionto "NuclearMagnetic Resonancein Chemistry" Ed. B. Pesce - Academic Press Inc. - Nev York - 1965 - p. 179.
6)
P. Bucci, J.Am.Chem.Soc.,PG, 252 (1968).
7)
T.W. Marshall and J.A. Pople, Mol.Phys.,1, 199 (1958).
8)
G. Del Be, J.Chem.Soc.,1958, 4031.
P)
G. Del Re, 8. Pullman and T. Yonezava,Biochim.andBiophysic.Acta,
IO)
W.
722 (1961).
2,
153
(1963).
l
Brugel, "NuclearMagnetic Resonancespectra and chemiaal structure"vol. I Academic Press - Nev York - London, 1967.
11) D.W. hathieson "Interpretationof organic spectra"- Academic Press Inc. - London, 1965. 12) H.L. Maddox, S.L. Staffordand H.D. Kaesz in "Advancesin organometallicchemistry" Edited by F.G.A. Stone and R. West - Academic Press - New York - London, 1965 - vol. 3.