Читать книгу Biochemistry For Dummies - John Moore T., Richard Langley H., John T. Moore - Страница 56

The presence of carbon-carbon double bonds leads to the possibility of having isomers present. Double bonds are rather restrictive and limit molecular movement. Groups on the same side of the double bond tend to remain in that position (cis), whereas groups on opposite sides tend to remain across the bond from each other (trans). See Figure 3-7 for an illustration of cis and trans isomers.

FIGURE 3-7: Cis and trans isomers.

If the two groups attached to either of the carbon atoms of the double bond are the same, cis-trans isomers aren’t possible. Cis isomers are the normal form of fatty acids, whereas food processing tends to convert some of the cis isomers to the trans isomers. The trans isomers are less biologically friendly (as in trans fats, which tend to be carcinogenic) than the cis isomers.

Cis-trans isomers are also possible in cyclic systems. The cis form has similar groups on the same side of the ring, whereas the trans form has similar groups above and below the ring.