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Investigation of Steric Features by Proton Magnetic Resonance.

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c1Capls
c[Capl,
c[CapJs
c[Und]3
c[Dod]z
cIB-A]~
c[B--SebJz
P 10.
M.p. [ "Cl
Crystal form
260
243
254
184
212
273
225
Needles
Triangular platelets
Needles
Needles
Needles
Needles
Needles
served depends on the position of the association equilibrium.
The shift is especially strong in arnines and is hardly affected
Rl
R2>: + H-CCls
R
R
'
;
P
:R ~ % - - H - C C ~ ~
R3'
by alkyl groups R provided the latter do not cause steric
hindrance to the association; for example, 6 = 520 cps in
methylamine. If the alkyl groups exert a steric effect, characteristic changes in the chemical shift occur.
The proton magnetic resonance of chloroform was measured
in various sterically hindered amines. The PMR signal varies
according to R within a range of 90 cps at 60 Mc. The
resonance frequencies bear a characteristic relationship to the
E, parameters of TUB [I], which give a measure of the steric
requirements of alkyl groups (see Table). A linear correlation is obtained which is simple to apply in order to determine steric parameters by proton magnetic resonance.
[Z 9/835 IE]
Received: June 2!st, 1965
German version: Angew. Chem. 77, 720 (1965)
[ l ] Oligomers and Pleionomers, Part 42. - Part 41: H. Zahn,
H . StoIper, and G . Heidemann, Chem. Ber., in the press.
[21 The following abbreviations are used:
Seb = -CO(CH~)8COCap = -NH(CH2)5COB
= -NH(CH2)6NHUnd
-NH(CH2)loCO= -CO(CH&CODod = -NH(CHZ)iiCO-.
A
[31 H. Zahn and G. B. Gleitsmann, Angew. Chem. 75,772 (1963);
Angew. Chem. internat. Edit. 2,410 (1963).
[4] M. Rofhe, 3. Polymer Sci. 30, 227 (1958).
[Sj P. Kusche, Doctorate Dissertation, Technische Hochschule
Aachen, 1963.
[6] G. B. Gleitsmann, Doctorate Dissertation, Technische Hochschule Aachen, 1962.
Investigation of Steric Features
by Proton Magnetic Resonance
By Dr. H. J. Friedrich
Table 1. Relationship between the chemical shift 6 of the PMR signal of
CHCI3 in amines and the Es parameters of Tuft [!I. The measurements
were made with approx. 0.5 % solutions of CHCI3 at 20 "C with
tetramethylsilane as internal standard in a Varian A 60 instrument.
RlRzRJN
gES
G[cpsat
60 Mc/s
R3
H
H
H
H
H
CH3
CzHs
H
H
CzHs
n-C3H7
n-C4H$
n-C4H9
i-C4H9
[a1 6 w 430 cps for CHCI, in indifferent solvents such as hexane.
Chemisches Institut der Universitat Wiirzburg (Germany)
Chloroform exhibits only a single proton magnetic resonance
signal in basic solvents owing to the formation of hydrogen
bonds with rapid proton exchange; the chemical shift ob-
Received: June 24th, 1965
IZ lZ/S3S IEl
German version: Angew. Chem. 77, 721 (1965)
[l] R . W . Tuft, J. Amer. chem. SOC.74, 3120 (1952).
CONFERENCE REPORTS
Meeting of South-West German Chemistry Lecturers
The meeting took place in Mainz (Germany) from April 28th
to 30th. Altogether 110 papers were presented, in part in
three parallel sessions. In order to avoid repetition of
publication, only those lectures will be summarized the
contents of which have not yet been published or submitted
for publication. The abstracts are arranged alphabetically
according to authors. For a subject index, see page 727 of
this issue.
I
The Polymerization of Isoprene Initiated by
Organolithiwn Compounds
isoprene are rate-determining. Solvation by ether reduces the
reactivity of the initiator. The overall reaction rate in ether
is therefore higher or lower than in heptane, depending on
the concentration [l] (double-dilatometer technique in the
range of low concentrations).
On the basis of the kinetic data and a postulated reaction
mechanism, a system of differential equations and equilibrium
relations was set up and solved numerically with an analogue
computer. The calculated conversion-time curves agreed up
to 90% conversion with the experimental curves within
the computing error of 1-3 %.
F. Bandermann and H. Sinn, Munchen (Germany)
Solutions of butyl-lithium in n-heptane were found to have
the resistances tabulated below (cell constant = 0.01 cm-1):
At initiator concentrations above 10-5 molejl in n-heptane,
ether, or mixtures of both, the concentrations of the undissociated monomeric organolithium compound and of the
[I] Cf. H . Sinn and F. Patat, Angew. Chem. 75, 805 (1963); Angew. Chern. internat. Edit. 3, 93 (1964); Fig. 1.
Angew. Chem. internat. Edit. 1 Vol. 4(1965)
1 No. 8
697
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investigation, features, sterin, magnetic, proto, resonance
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