Rau cov tshuaj tiv thaiv ntxiv, kev tsim ntawm ib qho tshuaj lom neeg los ntawm ob lossis ntau dua cov khoom pib yog tus yam ntxwv. Nws yog ib qho yooj yim los xav txog cov txheej txheem ntawm electrophilic sib ntxiv siv cov piv txwv ntawm alkenes - unsaturated acyclic hydrocarbons nrog ib tug ob daim ntawv cog lus. Ntxiv rau lawv, lwm cov hydrocarbons nrog ntau daim ntawv cog lus, suav nrog cov cyclic, nkag mus rau hauv cov kev hloov pauv no.
Cov kauj ruam ntawm kev sib cuam tshuam ntawm thawj molecules
Electrophilic ntxiv muaj nyob rau hauv ntau theem. Lub electrophile, uas muaj cov nqi zoo, ua raws li cov khoom siv hluav taws xob, thiab ob daim ntawv cog lus ntawm alkene molecule ua raws li cov khoom siv hluav taws xob. Ob lub tebchaw pib tsim qhov tsis ruaj khov p-complex. Tom qab ntawd qhov kev hloov pauv ntawm π-complex rau hauv ϭ-complex pib. Qhov tsim ntawm carbocation nyob rau theem no thiab nws txoj kev ruaj ntseg txiav txim siab tus nqi ntawm kev sib cuam tshuam tag nrho. Cov carbocation ces reacts sai nrog ib feem tsis zoo nqi nucleophile rau daim ntawvkawg khoom ntawm transformation.
Qhov cuam tshuam ntawm cov neeg hloov pauv ntawm cov tshuaj tiv thaiv tus nqi
Delocalization ntawm tus nqi (ϭ+) hauv carbocation nyob ntawm tus qauv ntawm tus thawj molecule. Cov txiaj ntsig zoo inductive nthuav tawm los ntawm pawg alkyl ua rau txo qis ntawm tus nqi ntawm cov pa roj carbon atom uas nyob ib sab. Yog li ntawd, nyob rau hauv ib tug molecule nrog ib tug electron-dawb hloov pauv, tus txheeb ze stability ntawm lub cation, lub electron ceev ntawm lub π-bond, thiab lub reactivity ntawm lub molecule raws li ib tug tag nrho nce. Cov nyhuv ntawm electron acceptors ntawm reactivity yuav opposite.
Halogen txuas mechanism
Cia peb txheeb xyuas kom ntxaws ntxiv txog cov txheej txheem ntawm cov tshuaj tiv thaiv electrophilic ntxiv uas siv cov piv txwv ntawm kev cuam tshuam ntawm alkene thiab halogen.
- Lub halogen molecule mus txog ob daim ntawv cog lus ntawm carbon atoms thiab dhau los ua polarized. Vim yog qhov zoo ib nrab ntawm ib kawg ntawm cov molecule, lub halogen rub cov electrons ntawm π daim ntawv cog lus ntawm nws tus kheej. Qhov no yog li cas qhov tsis ruaj tsis khov π-complex yog tsim.
- Ntawm cov kauj ruam tom ntej, cov khoom siv hluav taws xob ua ke nrog ob lub pa roj carbon atom, tsim ib lub voj voog. Ib tug cyclic "onium" ion tshwm.
- Cov seem uas tau them halogen particle (zoo them nucleophile) cuam tshuam nrog onium ion thiab koom rau sab nraud ntawm yav dhau los halogen particle. Cov khoom kawg tshwm sim - trans-1, 2-dihaloalkane. Ib yam li ntawd, qhov sib ntxiv ntawm halogen rau cycloalkene tshwm sim.
Mechanism ntawm kev sib ntxiv ntawm hydrohalic acids
Electrophilic ntxiv cov tshuaj tiv thaiv ntawm hydrogen halides thiab sulfuric acid ua txawv. Hauv nruab nrab acidic, cov reagent dissociates rau hauv cation thiab anion. Ib qho txiaj ntsig zoo ion (electrophile) tawm tsam π-bond, txuas mus rau ib qho ntawm cov pa roj carbon atom. Ib qho carbocation yog tsim nyob rau hauv uas cov pa roj carbon atom uas nyob ib sab yog zoo them. Tom ntej no, cov carbocation reacts nrog cov anion, tsim cov khoom kawg ntawm cov tshuaj tiv thaiv.
Cov kev taw qhia ntawm cov tshuaj tiv thaiv asymmetric thiab Markovnikov txoj cai
Electrophilic ntxiv ntawm ob lub asymmetric molecules ua tiav regioselectively. Qhov no txhais tau hais tias tsuas yog ib qho ntawm ob qhov ua tau isomers feem ntau yog tsim. Regioselectivity piav qhia Markovnikov txoj cai, raws li hydrogen txuas rau cov pa roj carbon atom txuas nrog ntau lwm cov hydrogen atoms (ntau dua hydrogenated).
Txhawm rau nkag siab qhov tseem ceeb ntawm txoj cai no, koj yuav tsum nco ntsoov tias cov tshuaj tiv thaiv yog nyob ntawm qhov ruaj khov ntawm cov carbocation nruab nrab. Cov txiaj ntsig ntawm electron-dawb thiab txais cov neeg hloov pauv tau tham saum toj no. Yog li, qhov sib ntxiv ntawm electrophilic ntawm hydrobromic acid rau propene yuav ua rau kev tsim ntawm 2-bromopropane. Ib qho nruab nrab cation nrog tus nqi zoo ntawm cov pa roj carbon atom hauv nruab nrab yog qhov ruaj khov dua li cov carbocation nrog cov nqi zoo ntawm cov atom sab nraud. Yog li ntawd, lub bromine atom cuam tshuam nrog lub thib ob carbon atom.
Qhov cuam tshuam ntawm kev rho tawm hluav taws xob hloov pauv ntawm kev sib cuam tshuam
Yog tias niam txiv molecule muaj cov khoom siv hluav taws xob rho tawm uas muaj qhov tsis zoo inductive thiab / lossis mesomeric effect, electrophilic ntxiv mus rau txoj cai saum toj no. Piv txwv ntawm cov khoom siv xws li: CF3, COOH, CN. Hauv qhov no, qhov kev ncua deb ntau dua ntawm cov nqi zoo los ntawm pawg electron rho tawm ua rau thawj carbocation ruaj khov. Yog li ntawd, hydrogen ua ke nrog cov pa roj carbon tsawg dua hydrogenated.
Txoj kev cai thoob ntiaj teb yuav zoo li no: thaum ib qho tsis sib haum xeeb alkene thiab cov tshuaj tsis sib haum xeeb, cov tshuaj tiv thaiv tau mus raws txoj hauv kev ntawm kev tsim cov carbocation ruaj khov tshaj plaws.
