Electrophilic tas li ntawd nyob rau hauv Organic Science News for KIDS

Rau ntxiv tshua tsiag ntawv los ntawm tsim tshuaj tebchaw los ntawm ob los yog ntau tshaj starting cov ntaub ntawv. Xav txog cov mechanism ntawm electrophilic tas li ntawd mus rau lub yooj yim piv txwv ntawm alkenes - unsaturated acyclic hydrocarbons nrog ib tug muab ob npaug rau daim ntawv cog lus. Nyob rau hauv tas li ntawd mus rau lawv, nyob rau hauv xws transformations noj lwm yam hydrocarbons muaj ntau yam bonds, xws li cyclic.

Cov qib reacting lub pib molecules

Electrophilic tas li ntawd yuav siv sij hawm qhov chaw nyob rau hauv ob peb ua sawv. Electrophile muaj ib tug zoo xwb ua raws li ib tug electron acceptor, thiab ob daim ntawv cog lus ntawm ib tug alkene molecule - raws li ib tug electron pub. Lub ob tebchaw tsim ib tug thawj p-volatile complex. Ces pib lub transformation ntawm π-complex nyob rau hauv ϭ-complex. Carbocation tsim nyob rau ntawm no theem thiab nws cov stability txiav txim seb tus nqi ntawm kev sis raug zoo nyob rau hauv feem ntau. Tom qab ntawd carbocation reacts sai heev nrog ib nrab tsis zoo them nucleophile thiab qhov kawg hloov dua siab tshiab khoom tsim.

Nyhuv ntawm substituents rau cov tshuaj tiv thaiv tus nqi

Them delocalization (ϭ +) nyob rau hauv carbocation nws nyob rau hauv lub pib molecular qauv. Zoo inductive nyhuv uas manifests alkyl pab pawg neeg, ua rau ib tug txo nyob rau hauv tus nqi uas nyob ib sab carbon atom. Raws li ib tug tshwm sim, nyob rau hauv lub molecule nrog electron tso substituent tsub kom tus kwv tij stability ntawm ntawv π-electron ceev yog vim thiab reactivity ntawm cov molecule raws li ib tug tag nrho. Ntxim rau cov reactivity ntawm electron acceptors yuav opposite.

Lub mechanism ntawm halogens kev twb kev txuas

Cia peb kawm nyob rau hauv ntau yam lub mechanism ntawm electrophilic ntxiv ntawm cov alkene rau ib qho piv txwv ntawm kev sis raug zoo thiab halogen.

1. Halogen molecule txuas ob daim ntawv cog lus ntawm cov pa roj carbon atoms thiab polarized. Vim lub cov zoo xwb nyob ib ncig ntawm lub qauv halogen cia li nkaum kiag lub electrons π-daim ntawv cog lus. Txij li thaum muaj ib tug tsim ntawm ib tug tsis ruaj tsis khov π-complex.
2. Nyob rau hauv lub kauj ruam tom ntej electrophilic particle kev cob cog rua rau ob carbon atoms, txoj kev ua ib lub nplhaib. Muaj yog ib tug cyclic "onium" ion.
3. Qhov seem them particle halogen (zoo them nucleophile) yog reacted nrog onium ion thiab koom nyob rau sab nraud ntawm lub yav dhau los hais halogen. Tshwm kawg khoom - trans-1,2-digalogenalkan. Ib yam li ntawd, Symptoms tshwm sim los ntawm halogen cycloalkenyl.

Lub mechanism Symptoms hydrohalic acids

Electrophilic tas li ntawd ntawm hydrogen halides thiab sulfuric acid tshwm sim lwm yam. Nyob rau hauv ib tug acidic ib puag ncig yog dissociated rau hauv ib tug ntawv thiab reagent anion. Zoo them ion (electrophile) noj cov π-daim ntawv cog lus ua ke rau ib qho ntawm cov pa roj carbon atoms. Carbocation yog tsim, nyob rau lub nyob ib sab carbon atom yog zoo them. Tom ntej no carbocation reacts nrog lub anion tsim qhov kawg khoom ntawm cov tshuaj tiv thaiv.

Cov kev taw qhia ntawm cov tshuaj tiv thaiv ntawm lub reagents thiab feem ntau asymmetrical Markovnikov

Electrophilic tas li ntawd ntawm ob asymmetric molecules tshwm sim regioselectively. Qhov no txhais tau hais tias ob isomers yog tsim dua ib tug. Regioselectivity piav Markovnikov tus txoj cai, raws li uas tus hydrogen yog txuas mus rau ib tug carbon atom kev cob cog rua nrog ib tug loj tus naj npawb ntawm lwm yam hydrogen atoms (ntau hydrogenated).

Yuav kom to taub txoj cai no, nws yog tsim nyog yuav tau nco qab hais tias cov tshuaj tiv thaiv tus nqi nyob rau hauv lub stability ntawm lub intermediate carbocation. Nyhuv ntawm electron pub thiab acceptor substituents hais saum toj no. Yog li, electrophilic tas li ntawd ntawm hydrobromic acid rau propene lead mus rau tsim ntawm 2-bromopropane. Lub intermediate ntawv nrog ib tug zoo xwb nyob rau hauv lub hauv paus carbon atom ruaj khov carbocation nrog ib tug zoo xwb nyob rau hauv cov huab atom. Raws li ib tug tshwm sim, ib tug bromine atom yog reacted nrog ib tug thib ob carbon atom.

Nyhuv ntawm electron-thim substituents rau hauv chav kawm ntawm lub sis

Yog hais tias tus thawj molecule muaj electron thau substituent uas muaj ib tug tsis zoo inductive thiab / los yog mesomeric nyhuv, electrophilic tas li ntawd yog tiv thaiv cov saum toj no kev cai. Piv txwv li substituents: CF _3, COOH, CN. Nyob rau hauv cov ntaub ntawv no, ntau dua qhov kev ncua deb ntawm qhov zoo xwb ntawm cov thawj electron thau pab pawg neeg ua rau ib tug ntau ruaj khov carbocation. Raws li ib tug tshwm sim, hydrogen kev cob cog rua rau cov atom tsawg hydrogenated.

Universal version ntawm cov kev cai yuav zoo li no: tus sis ntawm ib tug asymmetric alkene thiab ib tug asymmetric reagent cov tshuaj tiv thaiv tau nyaij los ntawm txoj kev ntawm tsim ntawm lub feem ntau ruaj khov carbocation.