Hayashi et al.
CHART 1
SCHEME 1. (A: pl), (A: pd), (B: pd), and (A′: pl′)
Structures, Together with Interconversion, in 1-4
SCHEME 2. p(Z)-π(C6H4)-p(Y) (Z ) O, S, Se, and Te)
Conjugations in (A: pl), (A: pd), and (B: pd) for 1-4
the p(Z)-π(Ar) conjugations are believed to decrease swiftly
as Z becomes heavier. How can the magnitudes of the
p(Z)-π(Ar) conjugation be elucidated? We searched for a
suitable system that enables us to clarify the magnitudes of the
p(Z)-π(Ar) conjugations.
9-(Arylchalcogenyl)triptycenes (p-YC6H4ZTpc (1-ArZTpc);
Z ) O (1),19 S (2), Se (3),20,21 and Te (4); Y ) H (a), NMe2
(b), OMe (c), Me (d), F (e), Cl (f), Br (g), COOEt (h), CN (i),
and NO2 (j)) are excellent candidates for that purpose (Chart
1). There are two conformers around the Z-CTpc bond in 1-4,
A and B:5c,6a-c,18,22 A corresponds to a conformer where the
Z-CAr bond is in the bisected area between two phenyl planes
of the triptycyl group, and B corresponds to a conformer where
the bond is on a phenyl plane of the triptycyl group. There are
also two conformers around the Z-CAr bond in 1-4, pl and
pd:5c,d,6a,c,18,23 pl corresponds to a conformer where the Z-CTpc
bond is in the Ar plane and it is pd if the bond is perpendicular
to the plane. Scheme 1 shows the (A: pl), (A: pd), and (B: pd)
conformers, together with the interconversion process in 1-4.19-21
Isolated rotation (IR) may occur around the Z-CAr bond,
converting (A: pl) into (A: pd), and thence into the equivalent
form (A: pl′) by further rotation of 180°, although (A: pl′) is
not shown in Scheme 1. There are three equivalent conforma-
tions in A. Similarly, three conformers are in B. Interconversion
between (A: pl) and (A′: pl′) may occur via (B: pd) where the
primes imply the topomeric structures (Scheme 1). This process
is referred to as gear rotation (GR).
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Very recently, some activation parameters were reported for
the IR and GR processes in 3 by analyzing the temperature
dependent 1H NMR spectra of 3a, 3c, 3i, and 3j, together with
the results of quantum chemical (QC) calculations on 3a, 3b′
(Y ) NH2), 3i, and 3j.21 The activation parameters change
depending on Y, although Y is limited. The results led us to
believe that the magnitudes of the p(Z)-π(C6H4)-p(Y) con-
jugation could be evaluated by analyzing the temperature
1
dependent H NMR spectra of 1-4. Scheme 2 illustrates the
orbital interactions of the p-YC6H4Z part in the triptycene
systems 1-4.
It is important to establish the (A: pl) structures of
p-YC6H4ZTpc in the ground state to analyze the temperature-
1
dependent H NMR spectra. The structures were determined
for 1a,j, 2a,j, and 9-benzyltriptycene (5a)19 by X-ray crystal-
lographic analysis, in addition to 3a-c,f,j.21 The temperature-
dependent 1H NMR spectra were measured and analyzed
carefully to evaluate the magnitudes of the p(Z)-π(C6H4)-p(Y)
conjugation for 2 and 3 having various Y in CD2Cl2. The
p(Z)-π(C6H4)-p(Y) conjugation must operate fully in (A: pl),
whereas the conjugation will not operate at all in (A: pd) and
(B: pd). The activation processes for IR and GR must contain
the loss of the p(Z)-π(C6H4)-p(Y) conjugation. Quantum
chemical (QC) calculations were also employed to analyze the
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4764 J. Org. Chem. Vol. 74, No. 13, 2009