preparation of cycloalkanes along their mechanism

preparation of cycloalkanes along their mechanism

Grade:12th Pass

1 Answers

askIITians Faculty 747 Points
8 years ago
The IUPAC system for naming cycloalkanes and cycloalkenes was presented in some detail in Sections 3-2 and 3-3, and you may wish to review that material before proceeding further. Additional procedures are required for namingThe equilibria (relative stabilities) and equilibration (rate of interconversion) of the rotational conformations of ethane and butane . If you review this material, it will be clear that forming a ring from a hydrocarbon chain will greatly reduce the number of possible staggered and eclipsed conformations.
Acycloalkaneis a regular alkane with a ring or loop. An example is cyclohexane, which is a ring of 6 carbon atoms, each bonded to 2 hydrogen atoms (C6H12).

The first thing to notice about cyclopropane and cyclobutane is thenon-ideal bond angles. The ideal bond angle in tetrahedral carbon is 109 degrees. However, constrained to a triangle and a square, the interior angles of cyclopropane (60 deg) and cyclobutane (90) are considerably less. This means that the electron clouds surrounding each atom will be considerably closer together than ideal, and sincelike charges repel, this will be energetically more unfavorable than for a straight-chain alkane. The additional instability caused by this constraint is calledangle strainorVon Baeyerstrain.
We briefly discussed cycloalkanes in thealkanesunit of this book, but in this unit, we'll be going into much greater detail about cycloalkanes as well as cycloalkenes. There are a number of properties that are unique to these structures and thus they deserve special attention.

Because of their cyclical nature, cycloalkanes do not have the freedom of rotation that regular alkanes possess. Stereochemistry plays a very important role in both the limitations of movements, but also, in some instances the limitations of reactions that can take place. Often these limitations are due less to the cyclical nature itself so much as the lack of freedom of rotation found in such alkanes.

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