Qhov Tseem Ceeb Qhov Sib Txawv - Qhov Kev Ntsuas Tus Kheej vs Cov Kev Ntsuas Kev Ntsuas
Qhov sib txawv tseem ceeb ntawm stereospecific thiab stereoselective cov tshuaj tiv thaiv yog tias, hauv cov tshuaj tiv thaiv stereospecific, sib txawv stereospecific reactants muab cov stereoisomer sib txawv ntawm cov khoom nyob rau hauv cov khoom zoo tagnrho (cov khoom yog tshwj xeeb rau stereoisomer ntawm cov reactant), whereas nyob rau hauv stereoselective cov tshuaj tiv thaiv, a ib qho reactant tuaj yeem muab ntau hom stereoisomers.
Stereochemistry yog ib feem ntawm chemistry uas cuam tshuam nrog peb-dimensional qauv ntawm cov molecules. Cov tshuaj tiv thaiv stereochemical tau muab faib ua ob pawg raws li stereospecific thiab stereoselective, raws li cov khoom siv stereochemistry. Cov khoom no hu ua stereoisomers.
Dab tsi yog Cov Lus Qhia Tshwj Xeeb?
Nyob rau hauv cov tshuaj tiv thaiv stereospecific, txhua tus stereoisomeric reactant tsim ib yam khoom stereoisomeric sib txawv los yog cov khoom sib txawv ntawm cov khoom stereoisomeric. Tag nrho cov tshuaj tiv thaiv stereospecific yog qhov tseem ceeb stereoselective, tab sis stereoselective cov tshuaj tiv thaiv tsis yog stereospecific. Piv txwv ntawm cov tshuaj tiv thaiv stereospecific suav nrog kev hloov pauv ntawm bromine mus rau (E)- thiab (Z) alkenes, cov tshuaj electrocyclic zoo li disrotatory nplhaib kaw, cheletropic syn-sib ntxiv ntawm singlet carbenes rau alkenes, thiab sigmatropic Claisen rearrangement ntawm cis- thiab trans- isomers ntawm (4S)-vinyloxypent-2-enes.
Daim duab 1: Lub Cev Muaj Zog Electrocyclic Ring Qhib
Nyob rau hauv tag nrho cov kev tshwm sim no, stereoisomeric substrates tau hloov mus rau stereoisomeric khoom. Nws tsis yog qhov yuav tsum tau ua rau cov tshuaj tiv thaiv kom 100% stereospecific. Yog hais tias ib qho tshuaj tiv thaiv ua kom sib xyaw ntawm ob qhov sib txawv stereoisomers hauv qhov piv ntawm 80:20, cov tshuaj tiv thaiv yog hu ua 80% stereospecific.
Dab tsi yog Qhov Kev Txiav Txim Siab Zoo?
Hauv cov tshuaj tiv thaiv stereoselective, ib qho reactant muab ob lossis ntau dua cov khoom steroisomeric, thiab ib yam khoom muaj txiaj ntsig ntau dua li lwm yam khoom lossis cov khoom lag luam. Cov tshuaj tiv thaiv stereoselective tuaj yeem piav qhia tau tias yog qhov nruab nrab stereoselective, siab stereoselective, lossis ua tiav stereoselective raws li qib ntawm kev nyiam rau ib qho tshwj xeeb stereoisomer.
Daim duab 02: D-A stereoselectivity
Stereoselective cov tshuaj tiv thaiv tshwm sim thaum sib ntxiv ntawm formic acid rau norbornene, diastereoselective txo ntawm 4-tert-butylcyclohexanone nrog lithum aluminium hydride, thiab enantioselective alkylation ntawm benzaldehyde nrog organozinc reagents nyob rau hauv lub xub ntiag ntawm (1R,, N-dibutylnorephedrine ua cov catalyst.
Qhov txawv ntawm Stereospecific thiab Stereoselective Reactions yog dab tsi?
Stereospecific vs Stereoselective Reactions |
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| Txhua tus stereoisomeric reactant tsim cov khoom sib txawv stereoisomeric lossis cov khoom sib txawv ntawm cov khoom stereoisomeric. | Ib tus reactant muab ob lossis ntau dua cov khoom steroisomeric, thiab ib yam khoom muaj txiaj ntsig ntau dua li lwm cov khoom lossis cov khoom lag luam. |
| kev sib raug zoo | |
| Txhua qhov kev xav tsis meej yog qhov tseem ceeb stereoselective. | Txhua qhov kev xav tsis zoo tsis yog qhov tseem ceeb stereospecific. |
| Examples | |
| trans-ntxiv ntawm bromine rau (E)- thiab (Z) alkenes, cov tshuaj electrocyclic zoo li disrotatory nplhaib kaw, cheletropic syn-ntxiv ntawm singlet carbenes rau alkenes, thiab sigmatropic Claisen rearrangement ntawm cis- thiab trans- isomers ntawm (4S)-vinyloxypent-2-enes | diastereoselective txo ntawm 4-tert-butylcyclohexanone nrog lithum aluminium hydride, thiab enantioselective alkylation ntawm benzaldehyde nrog organozinc reagents nyob rau hauv lub xub ntiag ntawm (1R, 2S)-N, N-dibutylnorephedrineua tus catalyst |
Summary – Stereospecific vs Stereoselective Reactions
Cov ntsiab lus ntawm stereoselective thiab stereospecific cov tshuaj tiv thaiv yog muab los ntawm kev soj ntsuam 3D qauv ntawm cov stereoisomers hauv cov tshuaj tiv thaiv stereochemical. Hauv cov tshuaj tiv thaiv stereospecific, txhua tus stereoisomeric reactant tsim cov khoom sib txawv stereoisomeric, whereas, nyob rau hauv cov tshuaj tiv thaiv stereoselective, ib qho reactant tuaj yeem tsim ob lossis ntau dua cov khoom stereoisomeric sib txawv. Qhov no yog qhov txawv ntawm stereospecific thiab stereoselective cov tshuaj tiv thaiv.
