7.2 The Stereogenic Center A carbon atom in a ring can be a stereogenic center if it bears two different sub- stituents and the path traced around the ring from that carbon in one direction is differ ent from that traced in the other. The carbon atom that bears the methyl group in 1, 2 epoxypropane, for example, is a stereogenic center. The sequence of groups is O-CH2 as one proceeds clockwise around the ring from that atom, but is CH2-O in the anti- clockwise direction. Similarly, C-4 is a stereogenic center in limonene models of the H2C—CHCH3 g By Modeling and 1-2-Epoxypropane Limonene (product of epoxidation of propene) (a constituent of lemon oil) PROBLEM 7. 2 Identify the stereogenic centers, if any, in (a)2-Cyclopenten-1-ol and 3-cyclopenten-1-ol SAMPLE SOLUTION (a)The hydroxyl-bearing carbon in 2-cyclopenten-1-oI is a stereogenic center. There is no stereogenic center in 3-cyclopenten-1-ol, since the sequence of atoms1→2→3→4→5 is equivalent regardless of whether one proceeds clockwise or anticlockwis H OH 2-Cyclopenten-1-ol enten -1-ol Even isotopes qualify as different substituents at a stereogenic center. The stereo- chemistry of biological oxidation of a derivative of ethane that is chiral because of deu terium(d=2H)and tritium (T= H) atoms at carbon, has been studied and shown to proceed as follows: CH Biological oxidation HO The stereochemical relationship between the reactant and the product, revealed by the isotopic labeling, shows that oxygen becomes bonded to carbon on the same side from hich is lost One final, very important point about stereogenic centers. Everything we have said in this section concerns molecules that have one and only one stereogenic cen ter, molecules with more than one stereogenic center may or may not be chiral. Mol- ecules that have more than one stereogenic center will be discussed in Sections 7.10 through 7.13 Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteA carbon atom in a ring can be a stereogenic center if it bears two different sub￾stituents and the path traced around the ring from that carbon in one direction is differ￾ent from that traced in the other. The carbon atom that bears the methyl group in 1,2- epoxypropane, for example, is a stereogenic center. The sequence of groups is O±CH2 as one proceeds clockwise around the ring from that atom, but is CH2±O in the anti￾clockwise direction. Similarly, C-4 is a stereogenic center in limonene. PROBLEM 7.2 Identify the stereogenic centers, if any, in (a) 2-Cyclopenten-1-ol and 3-cyclopenten-1-ol (b) 1,1,2-Trimethylcyclobutane and 1,1,3-Trimethylcyclobutane SAMPLE SOLUTION (a) The hydroxyl-bearing carbon in 2-cyclopenten-1-ol is a stereogenic center. There is no stereogenic center in 3-cyclopenten-1-ol, since the sequence of atoms 1 → 2 → 3 → 4 → 5 is equivalent regardless of whether one proceeds clockwise or anticlockwise. Even isotopes qualify as different substituents at a stereogenic center. The stereo￾chemistry of biological oxidation of a derivative of ethane that is chiral because of deu￾terium (D 2 H) and tritium (T 3 H) atoms at carbon, has been studied and shown to proceed as follows: The stereochemical relationship between the reactant and the product, revealed by the isotopic labeling, shows that oxygen becomes bonded to carbon on the same side from which H is lost. One final, very important point about stereogenic centers. Everything we have said in this section concerns molecules that have one and only one stereogenic cen￾ter; molecules with more than one stereogenic center may or may not be chiral. Mol￾ecules that have more than one stereogenic center will be discussed in Sections 7.10 through 7.13. C T H D CH3 C T HO D CH3 biological oxidation H 4 OH 3 5 2 1 2-Cyclopenten-1-ol H 4 3 5 2 OH 3 4 2 5 1 3-Cyclopenten-1-ol (does not have a stereogenic carbon) H2C CHCH3 O 1-2-Epoxypropane (product of epoxidation of propene) CH3 H 3 C 6 2 5 4 1 CH3 CH2 Limonene (a constituent of lemon oil) 7.2 The Stereogenic Center 263 Examine the molecular models of the two enantiomers of 1,2-epoxypropane on Learn￾ing By Modeling and test them for superposability. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website