lecture 4

lecture 4 - Chemistry 140A Fall 2008 (K. Albizati) Chapter...

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Chemistry 140A Fall 2008 (K. Albizati) 1 Chapter 4 – Cycloalkanes Because of the strength of the C-C bond, carbon chains can readily form ring-like structures or cycles. Such cyclic structures (when composed of only carbon atoms) are called cycloalkanes. Rings are very important substructures in organic and biochemistry. Practically all drugs contain at least one ring. CC C C H H H H H H H H H H HC C H H C H C H H H H H H C H H C H C H H H H Remove 2H's and form a C-C bond cyclic butane Cyclobutane each bend is a carbon Cyclooctane Cyclopropane The general formula for a cycloalkane in C n H 2n Nomenclature Look for the longest carbon chain and size of any rings. Whichever is larger, becomes the parent:
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Chemistry 140A Fall 2008 (K. Albizati) 2 Note that when there is only 1 substituent, there is no need to designate its position with a number. Suppose there are 2 substituents. To designate positions of substituents, number substituents in alphabetical priority using the lowest possible numbers. Number around the ring accordingly. 1-Ethyl-2-methylcyclopentane F 1-cyclopropyl-2-fluoro-4-propylcyclohexane
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Chemistry 140A Fall 2008 (K. Albizati) 3 Disubstituted and higher substituted rings can exist as “stereoisomers.” Stereoisomers have the same bond connectivity but differ in the arrangement of atoms in 3-dimensional space. Consider cyclopropane: Each carbon bears 2 hydrogens, one of which comes out at us from the plane of the board and one which goes back into the plane of the board. We can use dashed and wedged bond notation. H H H H H H The individual H’s do not interchange positions.
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lecture 4 - Chemistry 140A Fall 2008 (K. Albizati) Chapter...

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