Evans. Kim. Breit Cyclopropane: Bonding, Conformation, Carbonium lon Stabilization Chem 206 Cyclopropane Carbocation Stabilization via Cyclopropylgroups ■ Necessarily planar. Subtituents are therefore eclipsed a Disubstitution prefers to be trans ■ Almost sp2,not a rotational barrier of about NMR in super acids U=3080cm 13.7 kcal/mol is observed in 8(CH3)=2.6 and 3. 2 ppm following example Walsh Model for Strained Rings a Rather than o and gc-c bonds, cyclopropane has sp and p-type X-ray Structures support this orientation 1222A 1517A 1302A 1478A1474A 1464A 1541A t(antibonding 1409A 1444A Nonbonding A a-1(bonding) Angew Chem. Int Ed. 1979, 18, 809-826(handout R.F.Chds,JACS1986,108,1692H H H H H H Nonbonding Ph O H H Me Me C R O Evans, Kim, Breit Cyclopropane: Bonding, Conformation, Carbonium Ion Stabilization Chem 206 Cyclopropane ■ Necessarily planar. ■ Subtituents are therefore eclipsed. ■ Disubstitution prefers to be trans. u = 3080 cm-1 j = 120 ° ■ Almost sp2 , not sp3 Walsh Model for Strained Rings: ■ Rather than s and s* c-c bonds, cyclopropane has sp2 and p-type orbitals instead. side view s–1 (bonding) s (antibonding) s (antibonding) p (antibonding) p (bonding) p (bonding) 3 Carbocation Stabilization via Cyclopropylgroups A rotational barrier of about 13.7 kcal/mol is observed in following example: NMR in super acids d(CH3 ) = 2.6 and 3.2 ppm R. F. Childs, JACS 1986, 108, 1692 1.464 Å 1.409 Å 1.534 Å 1.541 Å 1.444 Å 1.302 Å 1.222 Å 1.474 Å 1.517 Å 1.478 Å X-ray Structures support this orientation de Meijere, "Bonding Properties of Cyclopropane & their Chemical Characteristics" Angew Chem. Int. Ed. 1979, 18, 809-826 (handout)