MAGNETIC RESONANCE IN CHEMISTRY
Magn. Reson. Chem. 2000; 38: 213–215
Reference Data
in new, environmentally safe syntheses of 2-naphthol,1 2-hydroxy-
6-isopropylnaphthalene2 and 2,6-dihydroxynaphthalene,3 which are
important compounds for the production of dyes, agrochemicals, drugs,
liquid-crystal materials and heat-resistant polymers. Alcohols 2, 5, 7
and 9 are by-products formed in the course of the oxidation of 1 or 4
by decomposition of the corresponding hydroperoxides, 7 also being a
promising starting material for liquid-crystal chemistry.
Among the aforementioned compounds, only 2-isopropylnaphthalene
is a relatively common compound, complete 13C and 1H spectral assign-
ments of which were made by Ernst and Schulz.4 Compounds 6 and 8
we have isolated for the first time only recently in our investigations on
the oxidation of 2-isopropyl- and 2,6-diisopropylnaphthalene.5
The hitherto unknown compounds 5 and 9 are described for the first
time in this paper. Taking into account the great practical importance of
2-isopropyl- and 2,6-diisopropylnaphthalene and their oxidation prod-
ucts, and also their possible derivatives, we report here their 13C and
1H spectral assignments and the incremental shifts of the isopropyl, 2-
hydroxy-2-methylethyl and 2-hydroperoxy-2-methylethyl substituents at
position 2 of the naphthalene ring.
Substituent effects on 13C and 1H chemical shifts in
2-isopropyl- and 2,6-diisopropylnaphthalene and
their oxidation products
∗
Roman Mazurkiewicz, Zbigniew Stec and
Jan Zawadiak
Institute of Organic Chemistry and Technology, Silesian
University of Technology, Krzywoustego 4, 44-100 Gliwice,
Poland
Received 22 July 1999; accepted 25 October 1999
ABSTRACT: 13C and 1H spectral assignments were made for three
2-substituted- and six 2,6-disubstituted naphthalenes with isopropyl,
2-hydroxy-2-methylethyl and 2-hydroperoxy-2-methylethyl substituents
by the use of proton–proton decoupling, 2D H,H-COSY and 2D-
C,H-COSY techniques. The downhill simplex method was used for
calculations of the best set of 13C and 1H incremental shifts. An excellent
additivity of substituent effects was found for both, the 13C and 1H
spectra of 2,6-disubstituted naphthalenes. Copyright 2000 John Wiley
& Sons, Ltd.
RESULTS AND DISCUSSION
Assignments of the 1H and 13C NMR spectra were made by the
use of proton–proton decoupling, 2D H,H-COSY and 2D C,H-COSY
techniques (Tables 1 & 2). In the case of three very close signals of C-3,
C-6 and C-7 in the 13C NMR spectrum of 2-isopropylnaphthalene (1)
we applied the reliable assignments given by Ernst and Schulz based
on the 2D INADEQUATE experiment.4
KEYWORDS: NMR; 13C NMR; 1H NMR; naphthalene derivatives; sub-
stituent effects; incremental shift calculation; downhill simplex method
The downhill simplex method6 was used to calculate 30 13C and
1
21 H incremental shifts for the naphthalene ring. The algorithm based
INTRODUCTION
on this method proved to be effective in finding the set of incremental
shifts which ensures the best fit of the experimental and the calculated
chemical shifts (Tables 3 and 4). In general, the method consists in the
multi-dimensional minimization of the function
2-Isopropylnaphthalene (1), 2,6-diisopropylnaphthalene (2) and their
oxidation products (2-hydroxy-2-methylethyl and 2-hydroperoxy-
2-methylethyl derivatives) are compounds of great interest for
modern chemical technology. The oxidation of 2-isopropylnaphthalene
and 2,6-diisopropylnaphthalene with oxygen in the liquid phase
to the corresponding hydroperoxides 3, 6 and 8 is a key step
X X
2
F.Zj,k/ D
.υei,j ꢀ υci,j
/
i
j
where Zj,k is the incremental shift brought about by the k-substituent
to position j of the naphtahalene ring, υei,j is the experimental chemical
shift for position j of the compound i and υci,j is the corresponding
chemical shift calculated according to the equation
X
υci,j D υnj C
Zj,k
where υnj is the chemical shift for position j of the naphthalene ring.
The standard deviations of the calculated values of the 13C and
1H chemical shifts in relation to the experimental data amount to
0.035 and 0.006 ppm, respectively. The 13C and 1H incremental shifts
for the isopropyl group obtained based on the NMR spectra of 2-
isopropylnaphthalene and three of its 2,6-derivatives are in good or
even very good agreement with the values given by Ernst and Schulz,4
which were calculated for 2-isopropylnaphthalene only.
The results obtained demonstrate both an excellent additivity of
effects of the substituents in 2,6-disubstituted naphthalene derivatives
and the adequacy of the downhill simplex method for calculations of
the incremental shifts.
EXPERIMENTAL
Spectra
NMR experiments were carried out on a Varian Unity INOVA-300
spectrometer operating at 300 or 75.5 MHz (for 1H and 13C, respectively)
using dilute solutions of the investigated compounds in CDCl3 (10 mmol
mlꢀ1) or saturated solutions of lower concentration in the case of
poorly soluble compounds 7, 8 and 9. NMR spectra were referenced
* Correspondence to: R. Mazurkiewicz, Institute of Organic Chemistry and
Technology, Silesian University of Technology, Krzywoustego 4, 44-100 Gliwice,
Poland.
Contract/grant sponsor: Ru¨tgers Kureha Solvents GmbH.
Copyright 2000 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2000; 38: 213–215
Mazurkiewicz, Roman
