Qhov Tseem Ceeb Qhov txawv - Electrophilic vs Nucleophilic Hloov
Electrophilic thiab nucleophilic hloov cov tshuaj tiv thaiv yog ob hom kev hloov pauv hauv chemistry. Ob qho kev hloov pauv electrophilic thiab nucleophilic hloov pauv cuam tshuam cuam tshuam nrog kev rhuav tshem ntawm daim ntawv cog lus uas twb muaj lawm thiab tsim kom muaj ib daim ntawv cog lus tshiab hloov daim ntawv cog lus dhau los; Txawm li cas los xij, qhov ntawd yog ua los ntawm ob txoj kev sib txawv. Hauv kev hloov pauv ntawm electrophilic, ib qho electrophile (ib qho zoo ion lossis qee qhov zoo kawg ntawm lub ncov qaumteb qabteb molecule) tawm tsam lub chaw electrophilic ntawm lub molecule whereas, nyob rau hauv nucleophilic hloov cov tshuaj tiv thaiv, ib tug nucleophile (electron nplua nuj molecular hom) tawm tsam lub nucleophilic chaw ntawm lub molecule rau tshem tawm pawg tawm. Qhov no yog qhov sib txawv tseem ceeb ntawm Electrophilic thiab Nucleophilic Hloov.
Electrophic hloov pauv yog dab tsi?
Lawv yog ib hom tshuaj tiv thaiv kab mob uas cov pab pawg ua haujlwm hauv ib qho chaw raug tshem tawm los ntawm electrophile. Feem ntau, hydrogen atoms ua raws li electrophiles hauv ntau cov tshuaj tiv thaiv. Cov tshuaj tiv thaiv no tuaj yeem muab faib ua ob pawg ntxiv; electrophilic aromatic hloov cov tshuaj tiv thaiv thiab electrophilic aliphatic hloov cov tshuaj tiv thaiv. Electrophilic aromatic hloov pauv tshwm sim tshwm sim hauv cov tshuaj tsw qab thiab siv los qhia cov pab pawg ua haujlwm rau benzene rings. Nws yog ib txoj hauv kev tseem ceeb hauv kev sib txuas cov tshuaj tshiab.
Electrophilic Aromatic Hloov
Nucleophilic hloov pauv yog dab tsi?
Nucleophilic hloov pauv cov tshuaj tiv thaiv yog thawj chav kawm ntawm cov tshuaj tiv thaiv uas cov khoom siv hluav taws xob nplua nuj nucleophile xaiv tawm tsam qhov zoo lossis qee qhov zoo ntawm cov atom lossis ib pawg ntawm atoms los tsim ib daim ntawv cog lus los ntawm kev hloov cov pawg sib txuas lossis atom. Cov pab pawg uas txuas yav dhau los, uas tawm ntawm cov molecule, hu ua "tawm pawg" thiab cov atom zoo lossis ib nrab zoo yog hu ua electrophile. Tag nrho cov khoom molecular suav nrog cov electrophile thiab cov pab pawg tawm mus yog hu ua "substrate".
General tshuaj formula:
Nu: + R-LG → R-Nu + LG:
Nu-Nucleophile LG-Tawm pab pawg
Nucleophilic Acyl hloov pauv
Qhov txawv ntawm Electrophilic thiab Nucleophilic Hloov pauv yog dab tsi?
Mechanism ntawm Electrophilic thiab Nucleophilic Hloov
Kev hloov hluav taws xob: Feem ntau ntawm cov kev hloov pauv hluav taws xob tshwm sim hauv lub nplhaib benzene nyob rau hauv lub xub ntiag ntawm ib qho electrophile (ib qho zoo ion). Lub tshuab yuav muaj ob peb kauj ruam. Ib qho piv txwv tau muab hauv qab no.
Electrophiles:
Hydronium ion H 3O + (los ntawm Bronsted acids)
Boron trifluoride BF 3
Aluminium chloride AlCl 3
Halogen molecules F 2, Cl 2, Br 2, Kuv 2
Nucleophilic Hloov: Nws koom nrog cov tshuaj tiv thaiv ntawm ib khub electron pub (tus nucleophile) thiab ib qho khoom siv hluav taws xob (cov electrophile). Lub electrophile yuav tsum muaj ib pab pawg tawm mus rau qhov tshwm sim.
Cov tshuaj tiv thaiv txheej txheem tshwm sim nyob rau hauv ob txoj kev: SN2 cov tshuaj tiv thaiv thiab SN1 cov tshuaj tiv thaiv. Hauv SN2 kev tawm tsam, kev tshem tawm ntawm pawg tawm thiab kev tawm tsam rov qab los ntawm nucleophile tshwm sim ib txhij. Hauv SN1 cov tshuaj tiv thaiv, lub hom phiaj carbenium ion tau tsim ua ntej thiab tom qab ntawd nws tau rov ua dua nrog cov nucleophile. Lub nucleophile muaj kev ywj pheej los tawm tsam los ntawm ob sab, thiab cov tshuaj tiv thaiv no cuam tshuam nrog racemization.
Piv txwv ntawm Electrophilic Hloov thiab Nucleophilic Hloov
Electrophic Hloov:
Cov kev hloov pauv hauv lub nplhaib benzene yog cov piv txwv ntawm cov tshuaj tiv thaiv electrophilic.
YNitration ntawm benzene
Nucleophilic Hloov:
Hydrolysis ntawm alkylbromide yog ib qho piv txwv ntawm Nucleophilic Hloov.
R-Br, nyob rau hauv cov xwm txheej yooj yim, qhov chaw tawm tsam nucleophile yog OH- thiab pab pawg tawm yog Br-.
R-Br + OH- → R-OH + Br-
Definition:
Recemization: racemization yog cov khoom siv kho qhov muag rau hauv qhov sib xyaw ua ke ntawm qhov sib npaug ntawm cov ntaub ntawv dextrorotatory thiab levorotatory.
