Geometry distorting intramolecular interactions to an alkyne group in 1-(2-aminophenyl)-2-(2-nitrophenyl)ethyne: a joint experimental? theoretical study

Abstract

X-Ray diffraction studies on the title compound show that in the crystalline state the amino and nitro groups lie to the same side of the triple bond and are hydrogen bonded to each other. There is a short contact to each alkyne carbon atom; one from a nitro oxygen atom, which leads to a trans bend in the alkyne, and one from an amino hydrogen atom. The analyses of the ab initio electron densities for this molecule and for its conformer with functional groups lying on opposite sides of the triple bond, using the theory of atoms in molecules, indicate that in both cases there is a bond path and associated (3, -1) critical point between the nitro oxygen atom and the nearer alkyne carbon atom, but not between the amino hydrogen atom and its alkyne carbon neighbour. Plots of the Laplacian for both conformers indicate local concentrations of 'lone-pair' density on the nitro oxygen atom, with local depletions in the valence shell charge concentration on the alkyne carbon atom, indicative of a nucleophile/electrophile type interaction. The geometry of the interaction of the alkyne with the amino hydrogen atom is far from optimal in the trans conformer.

Synthesis of 10‐Methylsulfide and 10‐Alkylmethylsulfonium nido‐Carborane Derivatives: B–H···π Interactions between the B–H–B Hydrogen Atom and Alkyne Group in 10‐RC≡CCH2S(Me)‐7,8‐C2B9H11

“…[35] However, despite the fact that intramolecular hydrogen bonding is one of the most studied noncovalent interactions of molecules, examples of intramolecular X-H···π(C≡C) hydrogen bonds are quite rare. In organic compounds, strong intramolecular X-H···π(C≡C) bonding was found in arylacetylenes containing NH- [36] or OH- [37] donor groups in the ortho-position, whereas for compounds with flexible chains such as 3-butyn-1-ol [38] or 3-hexyn-1,6-diol [39] the bonding is much weaker and results in mixtures of bonded and nonbonded conformers. Similar weak intramolecular C-H···π(C≡C) interactions were revealed in some aliphatic alkynes such as 1-pentyne and its derivatives.…”

Origins of the Helical Wrapping of Phenyleneethynylene Polymers about Single-Walled Carbon Nanotubes

“…Deviations of bond angles from their ideal values are well-known and have been addressed in the parametrization of the potential energy used in the simulations: 67 (a) the exocyclic angle where the alkyne is attached to a phenyl ring can exhibit deviations of several degrees from 120°, 87 and (b) the deviations from linearity of the bond angle that includes the two ethyne carbons of up to 8°a re consistent with both experimental and theoretical studies. 67,87,88 In addition, the internal rotation of one phenyl ring relative to another due to torsional rotation about the ethyne linkage is known to have a low barrier (0.6 kcal/mol), that is comparable to k b T at T = 300 K. 67,89−91 Thus, the phenyl rings can readily rotate so as to maintain van der Waals contact with the SWNT to accommodate helical superstructures. The underlying surface of the (10,0) SWNT is smooth and essentially featureless.…”

Stereoselective Total Synthesis of (−)‐Spirofungin A by Utilising Hydrogen‐Bond Controlled Spiroketalisation

“…[17] X-ray analysis and calculations conducted on tolan (diphenylethyne) derivatives indicate an increased "lone-pair" density on an oxygen atom and depletions in valence shell charge on the alkyne carbon atom. [18] A subtle increase in the electron density of the oxygen atom by this type of attractive interaction could account for the formation of an stronger intramolecular H-bond in isomer 4. The influence of the alkyne is further supported by the fact that there is no thermodynamic preference for spiroketal 16 (with a benzyloxymethyl group in place of the alkyne) indicating an absence of an H-bond effect as seen in 4 (Scheme 5).…”