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of symmetry is the trans -form of dimethyl-ketopiperazine. The, compound exists in two forms : cis and trans; the.cis-form has.na, 157, Stereochemistry, forms, but on the other hand the trans-form has a centre of sym-, Another important example of the conpound lhavinga contro, element of symmetry and hence exists in two enantiomorphle, Stereochemistry, anble, metry and, thepefore it is optically inactive., CH,, CH3, co-NH., CH, H, CO-NH, thentical and, of course, the mirror image, II, of the I. So t, NH-CO, H, cis-dimethyl ketopiperazine, | NH-CO, CHa, trans-dimethyl ketopiperazine having, centre of symmetry [ 1, H, Axis, CH3, Similarly, 1, 3-(di-sec.-butyl)-cyclobutanc and a-truxillic acid, are optically inactive,, Plane, CH3, CH3, COOH, H., H.C, CH3, H., CH3, COOH, CH3, HC, 1, 3-di-sec.-butyl cyclobutane, a-Truxillic acid, II, It must be noted that molecules with a plane of synımetry,, often also have a centre of symmetry.; furthermore, only even-, membered rings can possibly possess a centre of symmetry., Similarly, 3, 3-dichloro-3, 3-dimethylhexane is found to be, optically inactive due to the presence of two-fold alternating axis, of symmetry., A molecule is said to, (iii) Alternating axis of symmetry., possess an n-fold alternating axis of symmetry if, when it is rotated, through an angle of 360°ln about this axis and then reflected across, a plane perpendicular to the axis, an identical structure is obtained,, REDMI NOTE 8 PRO, 1. Note that in the formulae. the p toluene sulphonate ions are not shown., 88, Co AI QUAD CAMERA