Ch_322a_4.019 - and B rings in decalin shows cis-trans...

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Polycyclic Alkanes Polycyclic organic molecules are common in nature. For example, the steroid hormones (progesterone, testosterone, etc.) are polycyclic alkane derivatives. O CH 3 CH 3 CCH 3 O = H H H progesterone (pregnancy hormone) OH testosterone (male hormone) O CH 3 CH 3 H H H The steroid hormones are based on a polycyclic structure of 4 cycloalkanes referred to as the A,B,C and D rings. A B C D
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Some Stereochemical Features of Fused Cycloalkanes The A and B rings have stereochemical features of bicyclo[4.4.0]decane, commonly called "decalin." decalin bicyclo[4.4.0]decane The Decalins: Models for the A/B Ring Fusion The fusion of the
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Unformatted text preview: and B rings in decalin shows cis-trans isomerism. This isomerism is understandable as an extension of the isomerism in 1,2-dimethylcyclohexane. CH 3 CH 3 CH 3 CH 3 H H H H trans-1,2-diequatorial cis-1-equatorial-2-axial The Ring Fusions The trans and cis decalins are drawn by replacing the CH 3 groups with CH 2 groups and completing a second cyclohexane ring in a chair conformation. CH 2 CH 2 H H CH 2 CH 2 H H H H H H trans-decalin cis-decalin The H are on opposite sides. The H are on the same side. In the natural steroids, the trans A/B ring fusion is more common....
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