Pyramidal Alkene

In Cycloheptene (1.1) the Cis Isomer is an ordinary unstrained molecule but the heptane ring is too small to accommodate a trans configured alkene group resulting in strain and twisting of the double bond. The p-orbital misalignment is minimized by a degree of Pyramidalization .

Pyramidalized cage alkenes also exist where symmetrical bending of the substituents predominates without p-orbital misalignment.

The pyramidalization angle

\phi\

('''b''') is defined as the angle between the plane defined by one of the doubly bonded carbons and its two substituents and the extension of the double bond and is calculated as:

:

\ cos\phi\ =  -cos(R-C-C)/

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the butterfly bending angle or '''folding angle'''

\psi\

('''c''') is defined as the angle between two planes and can be obtained by averaging the two Torsional Angle s R1C:::CR3 and R2C:::CR4.

In alkenes 1.2 and '''1.3''' these angles are determined with X-ray Crystallography as respectively 32.4°/22.7° and 27.3°/35.6°. Although stable, these alkenes are very reactive compared to ordinary alkenes. They are liable to dimerization to Cyclobutadiene compounds or react with oxygen to Epoxide s.

In one study the strained alkene 3.4 was synthesized with the highest pyramidalizion angles yet, 33.5° and 34.3°. This compound is the double Diels-Alder adduct of the diiodide- Cyclophane '''3.1''' and Anthracene '''3.3''' by reaction in presence of Potassium Tert-butoxide in Reflux ing dibutyl ether through a di- Aryne intermediate '''3.2'''. This is a stable compound but will slowly react with oxygen to an Epoxide when left standing as a Chloroform solution.

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Pyramidal Alkene