Ntau qhov kev hloov pauv hloov qhib txoj hauv kev kom tau txais ntau yam sib txuas uas muaj kev siv nyiaj txiag. Lub luag haujlwm loj hauv kev tshawb fawb tshuaj thiab kev lag luam yog muab rau electrophilic thiab nucleophilic hloov pauv. Hauv kev tsim cov organic, cov txheej txheem no muaj ntau yam uas yuav tsum tau sau tseg.
Ntau yam tshuaj muaj tshwm sim. Hloov cov tshuaj tiv thaiv
Cov tshuaj hloov pauv cuam tshuam nrog kev hloov pauv ntawm cov tshuaj muaj qhov txawv ntawm ntau yam. Qhov kawg tshwm sim, thermal teebmeem yuav txawv; qee cov txheej txheem mus rau qhov kawg, hauv lwm cov tshuaj sib npaug tshwm sim. Ib qho kev hloov hauv cov khoom feem ntau yog nrog los ntawm kev nce lossis txo qis hauv qib oxidation. Thaum faib cov tshuaj phenomena raws li lawv qhov kawg tshwm sim, kev saib xyuas yog them rau qhov zoo thiab ntau qhov sib txawv ntawm cov reactants thiab cov khoom. Raws li cov yam ntxwv no, 7 hom tshuaj hloov pauv tuaj yeem paub qhov txawv, suav nrog kev hloov pauv, ua raws li cov tswv yim: A-B + C A-C + B. Cov ntaub ntawv yooj yim ntawm tag nrho cov chav kawm tshuaj phenomena muab lub tswv yim tias ntawm cov khoom pib muaj.hu ua "attacking" particle, hloov lub atom, ion, functional pab pawg nyob rau hauv lub reagent. Kev hloov pauv cov tshuaj tiv thaiv yog ib txwm muaj rau saturated thiab aromatic hydrocarbons.
Kev hloov pauv tuaj yeem tshwm sim hauv daim ntawv ntawm kev sib pauv ob npaug: A-B + C-E A-C + B-E. Ib qho ntawm cov subspecies yog kev hloov pauv, piv txwv li, tooj liab nrog hlau los ntawm kev daws ntawm tooj liab sulfate: CuSO4 + Fe=FeSO4 + Cu. Atoms, ions lossis pab pawg ua haujlwm tuaj yeem ua "kev tawm tsam" particle
Homolytic hloov pauv (radical, SR)
Nrog rau cov txheej txheem radical ntawm kev rhuav tshem covalent daim ntawv cog lus, ib khub electron uas muaj rau cov ntsiab lus sib txawv yog faib ua feem ntawm cov "fragments" ntawm cov molecule. Cov dawb radicals yog tsim. Cov no yog cov khoom tsis ruaj khov, qhov stabilization tshwm sim los ntawm kev hloov pauv tom ntej. Piv txwv li, thaum ethane tau los ntawm methane, cov dawb radicals tshwm sim uas koom nrog kev hloov pauv cov tshuaj tiv thaiv: CH4 CH3• + •H; CH3• + •CH3 → С2Н5; H• + •H → H2. Homolytic daim ntawv cog lus tawg raws li qhov muab hloov pauv mechanism yog yam ntxwv ntawm alkanes, cov tshuaj tiv thaiv yog saw. Hauv methane, H atoms tuaj yeem hloov pauv los ntawm chlorine. Cov tshuaj tiv thaiv nrog bromine tshwm sim zoo ib yam, tab sis iodine tsis tuaj yeem hloov ncaj qha hydrogen hauv alkanes, fluorine reacts heev nrog lawv.
Heterolytic txoj kev tawg daim ntawv cog lus
Nrog cov ionic mechanism ntawm kev hloov pauvelectrons yog unevenly faib ntawm cov tshiab tsim hais. Cov khub ntawm cov hluav taws xob sib txuas mus tag nrho mus rau ib qho ntawm "cov khoom tawg", feem ntau, mus rau tus khub ntawd, ntawm qhov tsis zoo nyob rau hauv cov polar molecule tau hloov. Kev hloov pauv muaj xws li tsim cov methyl cawv CH3OH. Nyob rau hauv bromomethane CH3Br, qhov cleavage ntawm cov molecule yog heterolytic, thiab cov nqi them yog ruaj khov. Methyl tau txais ib qho txiaj ntsig zoo, thiab bromine ua qhov tsis zoo: CH3Br → CH3+ + Br -; NaOH → Na+ + OH-; CH3+ + OH- → CH3OH; Na+ + Br- ↔ NaBr.
Electrophiles thiab nucleophiles
Cov khoom uas tsis muaj hluav taws xob thiab tuaj yeem txais lawv hu ua "electrophiles". Cov no suav nrog cov pa roj carbon atom txuas rau halogens hauv haloalkanes. Nucleophiles muaj cov khoom siv hluav taws xob ntau ntxiv, lawv "dawb" ib khub ntawm cov hluav taws xob thaum tsim cov khoom sib txuas. Hauv kev hloov pauv, nucleophiles nplua nuj nyob rau hauv cov nqi tsis zoo raug tawm tsam los ntawm electron starved electrophiles. Qhov tshwm sim no cuam tshuam nrog kev hloov pauv ntawm ib qho atom lossis lwm yam particle - cov pab pawg tawm. Lwm hom kev hloov pauv yog qhov kev tawm tsam ntawm electrophile los ntawm nucleophile. Tej zaum nws yog ib qho nyuaj rau kev paub qhov txawv ntawm ob txoj kev, los muab kev hloov pauv rau ib hom lossis lwm yam, vim nws nyuaj rau kev qhia meej meej uas ntawm cov molecules yog lub substrate thiab qhov twg yog cov reagent. Feem ntau, hauv cov xwm txheej zoo li no,cov hauv qab no yam:
- nature ntawm pawg tawm;
- nucleophile reactivity;
- nature ntawm cov kuab tshuaj;
- qauv ntawm alkyl ntu.
Nucleophilic hloov pauv (SN)
Nyob rau hauv cov txheej txheem ntawm kev sib cuam tshuam hauv cov organic molecule, kev nce hauv polarization yog pom. Hauv kev sib npaug, ib feem ntawm qhov zoo lossis qhov tsis zoo yog cim nrog tsab ntawv ntawm cov tsiaj ntawv Greek. Lub polarization ntawm daim ntawv cog lus ua rau nws muaj peev xwm txiav txim siab qhov xwm txheej ntawm nws txoj kev tawg thiab kev coj tus cwj pwm ntxiv ntawm "fragments" ntawm cov molecule. Piv txwv li, cov pa roj carbon atom hauv iodomethane muaj ib feem ntawm qhov zoo thiab yog qhov chaw electrophilic. Nws attracts ib feem ntawm cov dej dipole qhov twg oxygen, uas muaj ntau tshaj ntawm electrons, nyob. Thaum lub electrophile cuam tshuam nrog nucleophilic reagent, methanol tsim: CH3I + H2O → CH3 OH +HI. Nucleophilic hloov pauv tshwm sim tshwm sim nrog kev koom tes ntawm qhov tsis zoo ion lossis cov molecule uas muaj ib khub dawb electron uas tsis koom nrog hauv kev tsim cov tshuaj lom neeg. Kev koom tes nquag ntawm iodomethane hauv SN2-kev tshwm sim tau piav qhia los ntawm nws qhov qhib rau nucleophilic nres thiab kev txav ntawm iodine.
Substitution electrophilic (SE)
Ib qho organic molecule tuaj yeem muaj qhov chaw nucleophilic, uas yog tus cwj pwm los ntawm cov khoom siv hluav taws xob ntau dhau. Nws reacts nrog electrophilic reagent uas tsis muaj nqi tsis zoo. Xws li hais muaj xws li atoms nrog dawb orbitals, molecules nrog thaj tsam ntawm tsawg electron ceev. ATHauv sodium formate, carbon nrog "–" nqi cuam tshuam nrog qhov zoo ntawm cov dej dipole - nrog hydrogen: CH3Na + H2 O → CH 4 + NaOH. Cov khoom ntawm cov tshuaj tiv thaiv electrophilic no yog methane. Hauv cov tshuaj tiv thaiv heterolytic, cov chaw sib cuam tshuam ntawm cov organic molecules cuam tshuam, uas ua rau lawv zoo ib yam li ions hauv chemistry ntawm cov tshuaj inorganic. Nws yuav tsum tsis txhob raug saib xyuas tias kev hloov pauv ntawm cov organic tebchaw tsis tshua muaj nrog kev tsim cov cations tseeb thiab anions.
Monomolecular thiab bimolecular cov tshuaj tiv thaiv
Nucleophilic hloov pauv yog monomolecular (SN1). Raws li cov txheej txheem no, hydrolysis ntawm cov khoom tseem ceeb ntawm cov organic synthesis, tertiary butyl chloride, ua tiav. Thawj theem yog qeeb, nws yog txuam nrog gradual dissociation rau carbonium cation thiab chloride anion. Qhov thib ob theem yog sai dua, carbonium ion reacts nrog dej. Qhov sib npaug rau cov tshuaj tiv thaiv ntawm kev hloov cov halogen hauv ib qho alkane nrog ib pawg hydroxy thiab tau txais cov cawv thawj: (CH3)3C-Cl → (CH3)3C+ + Cl-; (CH3)3C+ +2O → (CH3)3C-OH + H+. Ib theem hydrolysis ntawm thawj thiab theem nrab alkyl halides yog tus cwj pwm los ntawm kev puas tsuaj ib txhij ntawm carbon-halogen daim ntawv cog lus thiab tsim ntawm C-OH khub. Qhov no yog cov txheej txheem ntawm nucleophilic bimolecular hloov pauv (SN2).
Heterolytic hloov pauv mechanism
Lub tshuab hloov pauv yog txuam nrog kev hloov ntawm ib qho hluav taws xob, kev tsimintermediate complexes. Cov tshuaj tiv thaiv ua sai dua, qhov yooj yim dua nws yog tsim cov khoom nruab nrab ntawm nws. Feem ntau cov txheej txheem mus rau ntau qhov kev qhia tib lub sijhawm. Qhov kom zoo dua yog feem ntau tau los ntawm txoj hauv kev uas cov khoom uas yuav tsum tau siv lub zog tsawg kawg nkaus rau lawv cov kev tsim. Piv txwv li, lub xub ntiag ntawm ob daim ntawv cog lus nce qhov tshwm sim ntawm qhov tshwm sim ntawm ib qho allyl cation CH2=CH-CH 2+, piv rau ion CH3+. Yog vim li cas nyob rau hauv lub electron ceev ntawm ntau daim ntawv cog lus, uas cuam tshuam rau delocalization ntawm tus nqi zoo dispersed thoob plaws hauv lub molecule.
Benzene hloov pauv cov tshuaj tiv thaiv
Pob ntawm cov organic tebchaw, uas yog tus cwj pwm los ntawm kev hloov pauv ntawm electrophilic - arenas. Lub nplhaib benzene yog lub hom phiaj yooj yim rau kev tawm tsam electrophilic. Cov txheej txheem pib nrog lub polarization ntawm daim ntawv cog lus nyob rau hauv lub thib ob reactant, uas ua rau tsim ib tug electrophile nyob ib sab ntawm lub electron huab ntawm lub nplhaib benzene. Qhov tshwm sim yog ib qho kev hloov pauv. Tseem tsis tau muaj kev sib txuas tag nrho ntawm cov khoom siv hluav taws xob nrog ib qho ntawm cov pa roj carbon atoms, nws yog attracted rau tag nrho cov nqi tsis zoo ntawm "sarmatic rau" ntawm electrons. Nyob rau theem thib peb ntawm cov txheej txheem, cov electrophile thiab ib qho carbon atom ntawm lub nplhaib txuas nrog ib khub ntawm electrons (covalent daim ntawv cog lus). Tab sis nyob rau hauv cov ntaub ntawv no, lub "aromatic rau" raug puas tsuaj, uas yog unfavorable los ntawm lub point ntawm view ntawm kev ua tiav ib tug ruaj khov sustainable zog lub xeev. Muaj ib qho tshwm sim uas tuaj yeem hu ua "proton ejection". H+ yog cais tawm, ruaj khovkev sib txuas lus tshwj xeeb rau arenas. Cov khoom los ntawm cov khoom lag luam muaj cov hydrogen cation los ntawm lub nplhaib benzene thiab anion los ntawm kev muaj pes tsawg leeg ntawm qhov thib ob reagent.
Piv txwv ntawm kev hloov pauv cov tshuaj tiv thaiv los ntawm cov khoom siv tshuaj lom neeg
Rau alkanes, kev hloov pauv cov tshuaj tiv thaiv tshwj xeeb yog yam ntxwv. Piv txwv ntawm kev hloov pauv ntawm electrophilic thiab nucleophilic tuaj yeem muab rau cycloalkanes thiab arenes. Cov tshuaj tiv thaiv zoo sib xws hauv cov molecules ntawm cov khoom siv organic tshwm sim nyob rau hauv ib txwm muaj, tab sis ntau zaus - thaum rhuab thiab muaj cov catalysts. Electrophilic hloov pauv nyob rau hauv lub aromatic nucleus yog ib qho ntawm cov txheej txheem dav thiab tau kawm zoo. Cov tshuaj tiv thaiv tseem ceeb tshaj plaws ntawm hom no yog:
- Nitration ntawm benzene nrog nitric acid nyob rau hauv muaj H2SO4 - mus raws li lub tswv yim: C 6 H6 → C6H5-NO 2.
- Catalytic halogenation ntawm benzene, tshwj xeeb yog chlorination, raws li kev sib npaug: C6H6 + Cl2 → C6H5Cl + HCl.
- Aromatic sulfonation ntawm benzene pib nrog "fuming" sulfuric acid, benzene sulfonic acids yog tsim.
- Alkylation yog hloov ntawm hydrogen atom los ntawm lub nplhaib benzene nrog alkyl.
- Acylation - tsim ntawm ketones.
- Formylation - hloov cov hydrogen nrog pawg CHO thiab tsim cov aldehydes.
Kev hloov pauv muaj xws li cov tshuaj tiv thaiv hauv alkanes thiab cycloalkanes, uas halogens tawm tsam C-H daim ntawv cog lus. Kev npaj ntawm derivatives tuaj yeem cuam tshuam nrog kev hloov pauv ntawm ib, ob lossis tag nrho cov hydrogen atoms nyob rau hauv saturated hydrocarbons thiabcycloparaffins. Ntau qhov hnyav molecular hnyav haloalkanes yog siv rau hauv kev tsim cov tshuaj ntau dua uas muaj nyob rau hauv cov chav kawm sib txawv. Cov kev kawm tiav hauv kev kawm txog cov txheej txheem ntawm kev hloov pauv hloov pauv tau muab lub zog muaj zog rau kev tsim cov khoom sib txuas raws li alkanes, cycloparaffins, arenes thiab halogen derivatives ntawm hydrocarbons.
