Cis<\/em> and trans<\/em> compounds have the same chemical formula but are shaped differently. With both cis<\/em> and trans<\/em>, a row of atoms experiences two irregularities.<\/p>\n The cis<\/em> pattern navigates the two irregularities in such a way that it ends up on the same side whence it started. The letter “c” is a good way to think of “cis”: the letter starts and ends at the right.<\/p>\n The trans<\/em> pattern ends up opposite whence it started. Letter “z” is a good illustration of the trans<\/em> pattern: it starts at the left, but ends at the right. <\/p>\n I’ve heard that trans<\/em> fat is to be avoided. (I’ve never heard that cis<\/em> is better, just that trans<\/em> is not preferred.) The reason, as I understand, is that trans<\/em> fat molecules, because of their zigzag geometry, stack alongside each other more easily than do cis<\/em> fat molecules. Since the trans<\/em> fat molecules stack together more easily, they can be more difficult to separate as well. Therefore, they have a stronger potential to form layers inside blood vessels.<\/p>\n Cis<\/em> and trans<\/em> are examples of isomerism. Isomers are molecules with the same formula but different arrangment of the atoms. Organic chemistry has so much focus on isomerism, I could easily write twenty posts about it. I may, in time….<\/p>\n HTH:)<\/p>\n Source:<\/p>\n Solomons, T.W. Graham. Organic Chemistry<\/u>, 4th ed. Toronto: John Wiley &Sons, 1988.<\/p>\n