Pericyclic Reactions - Notes | Harvard University

University:
Harvard University
Course:
CHEM 20 | Organic Chemistry
Academic year:

2023
Views:

263

Pages:

13
Author:

Dan Thompson

18Penisyclic ReactionsPericyclic Reactions are complex concertedxactions , however they are rare pericyclicreactions takes place through the formationof concerted From cyclic Transition state inwhich old bond breaking and new bond formationtakes place simultaniously The very commonexample is cyclisationCH2theCH2DoshuCHSH300of11CHCHH2CHCH2CH2H2DieneDienophileAddict(cyclohesene)These reactions are unaffected by any the polaritybonding but governed in periyelio Woodward by radical reactions - formation Hoffmaunwide takes placeThe according rule explain to the mechanism intracted of atoms possibilitytheof In bonding rule, between the orbital symmetry explainedin two ways ,the symmetry forbiddenis which theformationofintractionisnon- bordingbondingrestrictedand with repulsive state The second issymmetry allowed in which formation state. ofbonding favourable with attractivedecide the formation of banding anDuring intraction the outer orbitals and electronein woodward terminologyfrontier orbital FMO) and it is themechanism of pericyclic reactionsmain concept determining the concertedThe woodward -Hoffmann law having twomain concepts 7) are(1)The outer orbital which has to be intractedis known as highest occupied molecularorbital (HOMO) . The HOMO of one atomcan't intract the HOMO of secondatom since in this way the orbitalin a orbital and violation section ofoccupancy not more than two electronspaulils principlewattersTherefore the HOMO of one atom intractwith lowest unoccupied moluular orbital(LUMO) of second atom so, there shouldbe intraction is possible between HOMOLUMO but not HOMO w HOMO ih andLUMO10LUMO(2) In the intraction the overlapping oforbitals of intracted atoms shouldbe in same phase " The phase means the thelobe of one atom orbital overlapp only withsame the lobe of second atom obbitaloverlapp similarly in - -ve -ve lobe lobe of of one second atom atom orbitalorbitalphase and provide attraction for bondingThe overlapping is symmetry allowedforbidden and repulsion for non-bondingwhile overlapping out of phase is symmora .+Attraction