Cycloheptanes

Beginning with cycloheptane which has four conformations of similar energy confer matronal analysis of cycloalkanes becomes more complicated The same fundamental principles apply to medium and large rings as apply to smaller ones—but there are more atoms and more bonds to consider and more conformational possibilities... 

Cycloheptane or methyl benzoate -86° Methyl ethyl ketone... 

As ring size increases, there are progressively more conformations that need to be considered. For cycloheptane, four conformations have been calculated to be particularly stable. NMR investigations indicate that the twist-chair is the most stable. Various cycloheptane derivatives adopt mainly twist-chair conformations. ... 

Of alicyclic compounds, fluorination of cyclopentane and cyclohexane has been sufficiently investigated in the past. Cycloheptane on fluorination with cobalt trifluoride gives a mixture of highly fluorinated and perfluorinated cycloheptanes and methylcyclohexanes [/2] (equation 12). 

Electrostatic potential map for cycloheptane shows negatively-charged regions (in red) and positively-charged regions (in blue). 

When the chain bearing the allylsilane is one carbon longer, i.e., by the use of pentenylsilanes, cycloheptane rings can be formed. Both the (Z)- and (A )-isoiner of the (3-pentenyl)silanes can be synthesized selectively, but only the (Z)-(3-pentenyl)silane cyclized stereospecifically (complete 1,4-asymmetric induction). Both cthylaluminum dichloride and boron trifluoride diethyl ether complex promote the seven-membered ring formation35 43-48. 

Anomalous results were obtained in the cycloheptane series with butyllithium in which predominately trans-products were obtained16. 

In the cycloheptane series with butyllithium a 1 1 mixture of trans- and ew-adducts was obtained however phenyllithium gave predominately the //raw-product [(trans/cis) 95 5],6. Related studies have also been reported17,18. 

Brom-cycloheptan wird z. B. innerhalb 3 Stdn. bei 25° quantitativ zu Cycloheptan redu-ziert1. 

---