Abstract
The crystal structures of hexakis(dimethylamino)benzene (4) and its dication bis(triiodide) (8) have been determined. Crystals of 4 are monoclinic, space group C2/c, a = 18.440 (6) Å, b = 9.461 (3) Å, c = 12.017 (4) Å, β = 104.74 (3)°, Z = 4. Like hexaisopropylbenzene, hexakis(dimethylsilyl)benzene, and hexakis(dichloromethyl)benzene, molecules of 4 adopt approximate C 6h symmetry in the crystal, but, unlike these otherwise closely related compounds, 4 does not manifest an orientational disorder. Reaction of 4 with iodine yields 8, crystals of which belong to the monoclinic system, space group P2/c, a = 16.243 (5) Å, b = 11.051 (4) Å, c = 20.358 (7) Å, β = 112.02 (3)°, Z = 4. Molecules of 8 have crystallographic C 2 symmetry and approximate D 2 symmetry, with the benzene ring in a twist conformation. Variable-temperature NMR studies on 1,3,5-tris(diethylamino)-2,4,6-tris(dimethylamino)benzene (9) and hexakis(diethylamino)benzene, two molecules that are structurally related to 4, show that pyramidal inversion of the nitrogen atoms requires 8.2 and 10.0 kcal mol -1, respectively. As shown by the interconversion of the diastereomers of 1,3,5-tris(ethylmethylamino)-2,4,6-tris(dimethylamino)benzene, which requires 16.0 kcal mol -1, barriers to rotation about the C ar-N bonds in this class of compounds are substantially higher than barriers to pyramidal inversion. According to AM1 calculations, the homomerization (topomerization) of 4 is not concerted but involves stepwise inversion of the dimethylamino groups. The calculated activation energy, 10.5 kcal mol -1, is in reasonable agreement with the experimentally observed barrier of 8.2 kcal mol -1 for 9. Variable-temperature NMR studies on 8 reveal a site exchange of the methyl groups which is rationalized by a pseudorotational motion of the twisted benzene ring.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 3226-3232 |
| Number of pages | 7 |
| Journal | Journal of Organic Chemistry |
| Volume | 53 |
| Issue number | 14 |
| State | Published - 1988 |
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ASJC Scopus subject areas
- Organic Chemistry
Cite this
Stereochemistry of hexakis(dimethylamino)benzene and its dication. / Chance, Jeffrey M.; Kahr, Bart; Buda, Andrzej B.; Toscano, John P.; Mislow, Kurt.
In: Journal of Organic Chemistry, Vol. 53, No. 14, 1988, p. 3226-3232.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Stereochemistry of hexakis(dimethylamino)benzene and its dication
AU - Chance, Jeffrey M.
AU - Kahr, Bart
AU - Buda, Andrzej B.
AU - Toscano, John P.
AU - Mislow, Kurt
PY - 1988
Y1 - 1988
N2 - The crystal structures of hexakis(dimethylamino)benzene (4) and its dication bis(triiodide) (8) have been determined. Crystals of 4 are monoclinic, space group C2/c, a = 18.440 (6) Å, b = 9.461 (3) Å, c = 12.017 (4) Å, β = 104.74 (3)°, Z = 4. Like hexaisopropylbenzene, hexakis(dimethylsilyl)benzene, and hexakis(dichloromethyl)benzene, molecules of 4 adopt approximate C 6h symmetry in the crystal, but, unlike these otherwise closely related compounds, 4 does not manifest an orientational disorder. Reaction of 4 with iodine yields 8, crystals of which belong to the monoclinic system, space group P2/c, a = 16.243 (5) Å, b = 11.051 (4) Å, c = 20.358 (7) Å, β = 112.02 (3)°, Z = 4. Molecules of 8 have crystallographic C 2 symmetry and approximate D 2 symmetry, with the benzene ring in a twist conformation. Variable-temperature NMR studies on 1,3,5-tris(diethylamino)-2,4,6-tris(dimethylamino)benzene (9) and hexakis(diethylamino)benzene, two molecules that are structurally related to 4, show that pyramidal inversion of the nitrogen atoms requires 8.2 and 10.0 kcal mol -1, respectively. As shown by the interconversion of the diastereomers of 1,3,5-tris(ethylmethylamino)-2,4,6-tris(dimethylamino)benzene, which requires 16.0 kcal mol -1, barriers to rotation about the C ar-N bonds in this class of compounds are substantially higher than barriers to pyramidal inversion. According to AM1 calculations, the homomerization (topomerization) of 4 is not concerted but involves stepwise inversion of the dimethylamino groups. The calculated activation energy, 10.5 kcal mol -1, is in reasonable agreement with the experimentally observed barrier of 8.2 kcal mol -1 for 9. Variable-temperature NMR studies on 8 reveal a site exchange of the methyl groups which is rationalized by a pseudorotational motion of the twisted benzene ring.
AB - The crystal structures of hexakis(dimethylamino)benzene (4) and its dication bis(triiodide) (8) have been determined. Crystals of 4 are monoclinic, space group C2/c, a = 18.440 (6) Å, b = 9.461 (3) Å, c = 12.017 (4) Å, β = 104.74 (3)°, Z = 4. Like hexaisopropylbenzene, hexakis(dimethylsilyl)benzene, and hexakis(dichloromethyl)benzene, molecules of 4 adopt approximate C 6h symmetry in the crystal, but, unlike these otherwise closely related compounds, 4 does not manifest an orientational disorder. Reaction of 4 with iodine yields 8, crystals of which belong to the monoclinic system, space group P2/c, a = 16.243 (5) Å, b = 11.051 (4) Å, c = 20.358 (7) Å, β = 112.02 (3)°, Z = 4. Molecules of 8 have crystallographic C 2 symmetry and approximate D 2 symmetry, with the benzene ring in a twist conformation. Variable-temperature NMR studies on 1,3,5-tris(diethylamino)-2,4,6-tris(dimethylamino)benzene (9) and hexakis(diethylamino)benzene, two molecules that are structurally related to 4, show that pyramidal inversion of the nitrogen atoms requires 8.2 and 10.0 kcal mol -1, respectively. As shown by the interconversion of the diastereomers of 1,3,5-tris(ethylmethylamino)-2,4,6-tris(dimethylamino)benzene, which requires 16.0 kcal mol -1, barriers to rotation about the C ar-N bonds in this class of compounds are substantially higher than barriers to pyramidal inversion. According to AM1 calculations, the homomerization (topomerization) of 4 is not concerted but involves stepwise inversion of the dimethylamino groups. The calculated activation energy, 10.5 kcal mol -1, is in reasonable agreement with the experimentally observed barrier of 8.2 kcal mol -1 for 9. Variable-temperature NMR studies on 8 reveal a site exchange of the methyl groups which is rationalized by a pseudorotational motion of the twisted benzene ring.
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M3 - Article
VL - 53
SP - 3226
EP - 3232
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
SN - 0022-3263
IS - 14
ER -