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In the example below, the disrotation causes both methyls to point upwards, causing the product to be cis-dimethylcyclohexadiene. In addition, the torquoselectivity in an electrocyclic reaction refers to the direction of rotation. For example, a reaction that is conrotatory can still rotate in two directions, producing enantiomeric products.
A typical double bond consists of one sigma bond and one pi bond; for example, the C=C double bond in ethylene (H 2 C=CH 2). A typical triple bond, for example in acetylene (HC≡CH), consists of one sigma bond and two pi bonds in two mutually perpendicular planes containing the bond axis. Two pi bonds are the maximum that can exist between a ...
Numerous anomalous physical measurements, including bond lengths and dipole moments, have been examined through this concept. The original formulation of the Baker-Nathan effect is no longer employed due to more logical reasons for rate accelerations in solutions and its historical context is discussed by Saltzman.
In organic chemistry, an electrocyclic reaction can either be classified as conrotatory or disrotatory based on the rotation at each end of the molecule. In conrotatory mode, both atomic orbitals of the end groups turn in the same direction (such as both atomic orbitals rotating clockwise or counter-clockwise). In disrotatory mode, the atomic ...
Allylic strain – energetics related to rotation about the single bond between an sp 2 carbon and an sp 3 carbon. Atropisomerism – due to restricted rotation about a bond. Folding, including the secondary and tertiary structure of biopolymers (nucleic acids and proteins). [11] Akamptisomerism – due to restricted inversion of a bond angle.
For example, the absorption spectrum for ethane shows a σ → σ* transition at 135 nm and that of water a n → σ* transition at 167 nm with an extinction coefficient of 7,000. Benzene has three aromatic π → π* transitions; two E-bands at 180 and 200 nm and one B-band at 255 nm with extinction coefficients respectively 60,000, 8,000 and 215.
The structure of pi bonds does not allow for rotation (at least not at 298 K), so the double bond and the triple bond which contain pi bonds are held due to this property. The sigma bond is not so restrictive, and the single bond is able to rotate using the sigma bond as the axis of rotation (Moore, Stanitski, and Jurs 396-397). Another ...
As a result, pi–pi and cation–pi interactions are important factors in rational drug design. [24] One example is the FDA-approved acetylcholinesterase (AChE) inhibitor tacrine which is used in the treatment of Alzheimer's disease. Tacrine is proposed to have a pi stacking interaction with the indolic ring of Trp84, and this interaction has ...