5.5 Physical Properties of Alkenes TABLE 5.1 Cahn-Ingold-Prelog Priority Rules 1. Higher atomic number takes precedence over The compound lower Bromine(atomic number 35)outranks chlor- ine(atomic number 17). Methyl(C, atomic number 6) Higher Br Higher outranks hydrogen (atomic number 1) Lower Lower has the Z configuration. Higher ranked atoms(Br and C of CHa)are on the same side of the double bond 2. When two atoms directly attached to the double The compound bond are identical, compare the atoms attached with these two on the basis of their atomic numbers pre-. Higher Br CH Lower cadence is determined at the first point of difference Ethyl[一c(c,H,H】] outranks methyl[c(HHH) Lower CH2CH Hiaher has the E configuration Similarly, tert-butyl outranks isopropyl, and isopropyl outranks ethyl C(CH3)3>—CH(CH3)2>—CH2CH C(C, CC)>-C(C, C, H)>-C(C, H, H) 3. Work outward from the point of attachment, com- The compound paring all the atoms attached to a particular atom before proceeding further along the chain Higher Br CH2CH2OH Lower -CH(CH3)2[C(CC, H) outranks CH2CH2OH [C(C, H, H)I Lower CH(CH3)2 Higher has the E configuration 4. When working outward from the point of attach The compound ment, always evaluate substituent atoms one by one, never as a group. Since oxygen has a higher atomic Higher B CH2OH Higher -CH,OH [C(O, H, H outranks Lowe C(CH3)3 Lower C(CH)3[-c(C, C, o) has the Z configuration 5. An atom that is multiply bonded to another atom The compound is considered to be replicated as a substituent on that atom: Higher CH2OH Lower Lower CH=O Higher s treated as if it were CO,, H) group-CH=o [-C(o, O, H)] outranks-CH2OH has the E configuration C(O,H, H) Back Forward Main MenuToc Study Guide ToC Student o MHHE Website5.5 Physical Properties of Alkenes 175 TABLE 5.1 Cahn–Ingold–Prelog Priority Rules Rule 1. Higher atomic number takes precedence over lower. Bromine (atomic number 35) outranks chlor￾ine (atomic number 17). Methyl (C, atomic number 6) outranks hydrogen (atomic number 1). 2. When two atoms directly attached to the double bond are identical, compare the atoms attached with these two on the basis of their atomic numbers. Pre￾cedence is determined at the first point of difference: 3. Work outward from the point of attachment, com￾paring all the atoms attached to a particular atom before proceeding further along the chain: 4. When working outward from the point of attach￾ment, always evaluate substituent atoms one by one, never as a group. Since oxygen has a higher atomic number than carbon, Example The compound has the Z configuration. Higher ranked atoms (Br and C of CH3) are on the same side of the double bond. The compound The compound The compound has the Z configuration. has the E configuration. Similarly, tert-butyl outranks isopropyl, and isopropyl outranks ethyl: Higher Lower Higher Lower Br Cl CH3 H C C Higher Lower Lower Higher Br Cl CH3 CH2CH3 C C has the E configuration. Higher Lower Lower Higher Br Cl CH2CH2OH CH(CH3)2 C C Higher Lower Higher Lower Br Cl CH2OH C(CH3)3 C C Ethyl [±C(C,H,H)] The group ±CHœO [±C(O,O,H)] outranks ±CH2OH [±C(O,H,H)] ±CH(CH3)2 [±C(C,C,H)] ±CH2CH2OH [±C(C,H,H)] outranks methyl [±C(H,H,H)] outranks ±CH2OH [±C(O,H,H)] ±C(CH3)3 [±C(C,C,C)] outranks 5. An atom that is multiply bonded to another atom is considered to be replicated as a substituent on that atom: The compound has the E configuration. Higher Lower Lower Higher Br Cl CH2OH CH C C O ±CH is treated as if it were ±C(O,O,H) X O ±C(CH3)3  ±CH(CH3)2  ±CH2CH3 ±C(C,C,C)  ±C(C,C,H)  ±C(C,H,H) Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website