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Karplus Curve for 3J(13C 1H) in Hydrocarbons.

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spectral habit they can be assigned to a 3 : 1 mixture (integration) of diastereomeric forms of the diphosphaguanidine 2 with fixed CN double bond. Formation and equilibrium behavior of the two silatautomers 1 + 2 were substantiated by the following findings.
When solid 1, cooled to -9O"C, is dissolved in CD2C12
and measured without interruption of the cooling track at
-9O"C, its isomer 2 is detectable in the 3'P{'H}-NMR
spectrum below O"C, i.e. still no silyl migration occurs up
to this temperature. The signal of 2 appears at 6 = -23
only above this limiting temperature. The temperature-dependent sequence of spectra is reversible. Moreover, on
comparison of Figure l a with l b and lc, the reverse broadening of the signals of 1 and 2 indicates the presence of a
dynamic equilibrium within the NMR time scale.
In the spectrum of the methylphosphane 1 below
- 30 " C , an increasing differentiation of the original AB
multiplet (Fig. le, f) can be recorded which could be due
to a previously unobserved, special conformational characteristic at the methylene carbon. By comparative investigations on authentic E / Z pairs of similarly structured phosphaalkenes[21we might possibly establish that this signal
doubling is not just caused by the Z isomer, but by rotamers-presumably at the CN bond"'.
The silatropism is reminiscent of the equilibrium behavior of doxy-substituted derivatives of l L 4 I ; both phenomena-silatropism and hindrance to rotation-are known
for (silyl)-carboxamides'51.
Table 1. 'J("C,'H) [Hz] in norbornane; pertinent CCCH torsion angles 4
in parentheses.
c-2
c-3
c-4
c-7
-
6.76 (154)
8.75 (180)
-
-
-
2.21 (65)
-
-
8.54(172)
-
-
3
-
-
4
-
-
1.06 (120)
2.36 (121)
-
8.78 (170)
5.28 (20)
i5: 0 (85)
7.08 (155)
electron diffraction measurements['I. The dependence of
3J('3C,'H) values on Q can be described by the function
3J( I3C,'H)= 3.81 - 0 . 9 0 ~ 0 ~ 03.83
+ ~ 0 ~ 2 4
(a)
which is displayed graphically in Figure 1. Excellent agreement with the results of calculations on propane is
foundL5].Hence, bearing in mind the known reservations"],
eq. (a) can be used for the conformational analysis of hydrocarbons and serves as a basis for the study of substituent effects on 3J(13C,'H).
7.0
[ I ] H. Kessler, G. Zimmermann, H. Forster, J. Engel, G. Oepen, W. S. Sheldrick, Angew. Chem. 93 (1981) 1085: Angew. Chem. In!. Ed. Engl. 20
(1981) 1053.
121 R. Appel, F. Knoll, I. Ruppert, Angew. Chem. 93 (1981) 771; Angew.
Chem. Inr. Ed. Engl. 20 (1981) 731.
131 The freezing-in of the pyramidal inversion at the N- and phosphane-P
6.0
5.0
4 .O
3.0
atom could likewise lead to diastereomer formation.
141 G. Becker, 2. Anorg. Allg. Chem. 423 (1976) 242.
[5] a) M. Fukui, K. Itoh, Y. Ishii, J. Chem. Soc. Perkin Trans. 2 (1972) 1043;
b) E. Breitmaier, W. Voelter: "C-NMR-Spectroscopy. Methods and Applicafirtns. 2nd Edit., Verlag Chemie, Weinheim 1978, p. 86.
2 .o
1.0
0"
30"
60"
90"
120"
150" 180"
Fig. 1. Dependence of 'J('T,'H) in norbornane on the torsion angle:
perimental, - calculated from eq. (a).
Karplus Curve for
3J('3C,'H) in Hydrocarbons**
By Rafet Aydin, Jean-Pierre Loux, and
Harald Giinther*
Of the various NMR spin-spin coupling constants, particularly those between vicinal nuclei are of importance for
conformational analysis, due to their torsional angle dependence postulated by Karplus and verified experimenhas been
tally. Whereas the Karplus curve for 3J(1H,1H)111
thoroughly investigated, this is not the case for
3J( I3C,'H)[']; specifically, until now hydrocarbons have not
been studied. We therefore synthesized the deuterated norbornanes 1-4 and calculated the I3C,'H coupling constants from the measured I3C,'H coupling constants['] using the well-known relationship
"J("C,'H)=6.5144 "J(I3C,*H)
The 3J('3C,'H) values of interest here are shown in Table 1
together with the CCCH torsion angles Q determined by
J.-P. Loux, Dr. R. Aydin
Universitat-Gesamthochschule,Fachbereich 8, OC 11
[*] Prof. Dr. H. Giinther, Dr.
Postfach 21 0209, D-5900 Siegen 21 (Germany)
ex-
Received: February I I, 1982 [Z 115 IE]
German version: Angew. Chem. 94 (1982) 451
[I] M. Karplus, J. A m . Chem. SOC.85 (1963) 2870.
[2] P. E. Hansen, B o g . Nucl. Magn. Reson. Specfrosc. 14 (1981) 175.
131 R. Aydin, H. Giinther, 2. Narurforsch. 8 3 6 (1981) 398.
[41 Y. Yokozeki, K. Kuchitsu, Bull. Chem. SOC.Jpn. 44 (1971) 2356.
[5] R. Wasylishen, T. Schaefer, Can. J. Chem. 51 (1973) 961; M. Barfield,
J. A m . Chem. SOC.102 (1980) I .
"Contra-Steric" Alkylation of the Enolates of
Dioxolanecarboxylic Acid Esters
By Wolfgang Ladner*
The deprotonation of the trans-substituted dioxolanes
(tartrate acetonides) 1 to yield the enolates 2 has recently
been described"]. On reaction with electrophiles these
enolates gave preferentially the isomers 3. Hence, the substitution 1-3 corresponds stereochemically to a retention.
[*I W. Ladner
[**I This work was supported by the Deutsche Forschungsgemeinschaft and
Angew. Chem. Inr. Ed. Engl. 21 (1982) No. 6
C-6
1
2
Received: February 12, 1982 [Z 110 IE]
German version: Angew. Chem. 94 (1982) 460
the Fonds der Chemischen Industrie.
c-5
["I
Fachbereich Chemie der Universitat
Hans-Meerwein-Strasse, D-3550 Marburg (Germany)
0 Verlag C h e m h GmbH. 6940 Weinheim. 1982
0570-0833/82i0606-0449 ?
02.50/0
i
449
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