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Natural bond orbital (NBO) analysis of C 4 H 4 BH has been performed in order to understand the bonding of borole in the familiar Lewis picture. [5] According to the computational results, the occupancy of the two C−C π orbitals is about 1.9, with a tiny amount of electronic charge (an occupancy of 0.13) delocalised on the out-of-plane boron p orbital, illustrated below.
The π system of furan and lone pairs. Note that one of the oxygen lone pairs participates in conjugation in a p orbital, while the other lone pair is in an sp 2 hybridized orbital in the plane of the molecule and not part of the π system. The participation of six electrons in the π system makes furan aromatic (see below).
For this molecule, carbon sp 2 hybridises, because one π (pi) bond is required for the double bond between the carbons and only three σ bonds are formed per carbon atom. In sp 2 hybridisation the 2s orbital is mixed with only two of the three available 2p orbitals, usually denoted 2p x and 2p y. The third 2p orbital (2p z) remains unhybridised.
Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as furans. Furan is a colorless, flammable, highly volatile liquid with a boiling point close to room temperature.
For example, the C−H bond length is 110.2 pm in ethane, 108.5 pm in ethylene and 106.1 pm in acetylene, with carbon hybridizations sp 3 (25% s), sp 2 (33% s) and sp (50% s) respectively. To determine the degree of hybridization of each bond one can utilize a hybridization parameter (λ).
Heteroarenes are aromatic compounds, where at least one methine or vinylene (-C= or -CH=CH-) group is replaced by a heteroatom: oxygen, nitrogen, or sulfur. [3] Examples of non-benzene compounds with aromatic properties are furan, a heterocyclic compound with a five-membered ring that includes a single oxygen atom, and pyridine, a heterocyclic compound with a six-membered ring containing one ...
In this situation the oxygen is sp 3 hybridized according to valence bond theory. Increasing the bond order to two by involving another lone pair changes the hybridization at the oxygen to an sp 2 center with an expected expansion in the M-O-R bond angle and contraction in the M-O bond length. If all three lone pairs are included for a bond ...
The best-known example is benzene (C 6 H 6) with a conjugated system of six π electrons, which equals 4n + 2 for n = 1. The molecule undergoes substitution reactions which preserve the six π electron system rather than addition reactions which would destroy it. The stability of this π electron system is referred to as aromaticity. Still, in ...