Photo‐CIDNP in the Vacuum‐UV: Di‐<i>tert</i>‐butyl Ether and 2,2,5,5‐Tetramethyltetrahydrofuran in Aqueous Solution

The crystal structures of methyl 4‐methoxycubane‐1‐carboxylate (1), 1‐acetamido‐4‐fluorocubane (2), methyl 4‐acetoxycubane‐1‐carboxylate (3), 1,4‐difluorocubane (4), 1,4‐dichlorocubane (5), and N,N‐diisopropylcubane‐1,4‐dicarboxamide (6) have been investigated by means of X‐ray diffraction analysis. Fluorine and chlorine substituents cause a shortening of the vicinal bonds, as is seen in the 4‐halocubane‐1‐carboxylates. The cage bonds vicinal to the ester substituent, with a favorable orientation with regard to the π‐acceptor influence of this group become longer than the CH–CH bonds. Furthermore, the influence on bond length with respect to the orientation of this group relative to bonds within the cubane skeleton has been investigated experimentally. The effect of the methoxy group has also been found to depend on the orientation. The cage bond antiperiplanar to the methyl group is shortened, while the cage bonds in gauche orientation to this group are lengthened. As seen in the case of the halogen‐substituted derivatives, the bonds bearing the acetoxy substituent are shortened due to the σ‐acceptor property of this group. Ab initio calculations on compounds 1, 2, 4, and 5 performed at the 6‐31G* level confirm the experimental results.

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The Cubane Cage – A Sensitive Probe for Assessing Substituent Effects on a Four-Membered Ring, Part II

Irngartinger¹,

Strack

Gredel

et al. 1999

Eur. J. Org. Chem.

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Substituent-Dependent Formation of Supramolecular Aggregates of 6-Hydroxy-trans-3-hexenoic Acids in the Solid State

Strauch

Rinderknecht

Erker³

et al. 2000

Eur. J. Org. Chem.

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Packing Modes in Some Mono‐ and Disubstituted Phenylpropiolic Acids: Repeated Occurrence of the Rare syn,anti Catemer

Das

Desiraju

2006

Chemistry An Asian Journal

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The catemer is an infinite one-dimensional pattern formed by the carboxylic acid group in crystals, and is constituted with O-H...O hydrogen bonds. The catemer is uncommon and may be contrasted with the ubiquitous carboxylic acid dimer, the favored mode of association of this functional group. Both catemers and dimers, however, have two O-H...O hydrogen bonds for each carboxy group, so the reasons for the rarity of the catemer must lie elsewhere. In this paper, we describe a group of around 25 phenylpropiolic acids in which the catemer is the default packing mode. Exceptionally, the particular catemer that is found in this family is of the very rare syn,anti variety. We show that a necessary ingredient in catemer formation is a supportive C-H...O hydrogen bond from a proximal C-H group, which is located on the phenyl ring, ortho to the ethynyl group, and suitably activated by electron withdrawing substituents. When steric factors become noteworthy, alternative patterns are adopted, such as the syn,syn catemer and, in one case, a rare cisoid dimer. When electron-donating groups, either through inductive effect such as methyl or through resonance such as halogens, are present on the phenyl ring, the dimer is formed in all but one case. Polymorphism seems not to be an issue in these carboxylic acids in that no compound would generally crystallize as both a dimer and a catemer. It may be concluded that a supporting interaction, in this case a C-H...O hydrogen bond, is the essential condition for the formation of any carboxylic acid catemer. Catemers are so rare because it is difficult to set up this type of supporting interaction in most carboxylic acids.

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Photo‐CIDNP in the Vacuum‐UV: Di‐tert‐butyl Ether and 2,2,5,5‐Tetramethyltetrahydrofuran in Aqueous Solution

Cited by 4 publications

References 11 publications

The Cubane Cage – A Sensitive Probe for Assessing Substituent Effects on a Four-Membered Ring, Part II

The Cubane Cage – A Sensitive Probe for Assessing Substituent Effects on a Four-Membered Ring, Part II

Substituent-Dependent Formation of Supramolecular Aggregates of 6-Hydroxy-trans-3-hexenoic Acids in the Solid State

Packing Modes in Some Mono‐ and Disubstituted Phenylpropiolic Acids: Repeated Occurrence of the Rare syn,anti Catemer

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