Hloov tshua: hauj lwm, kab zauv piv txwv

Muaj ntau hloov cov tshuaj tiv thaiv yuav qhib txoj kev rau qhov kev npaj ntawm ntau yam tebchaw muaj nqi hluav taws xob daim ntawv thov. Ib tug loj loj luag hauj lwm nyob rau hauv cov tshuaj science thiab kev lag luam yog muab electrophilic thiab nucleophilic hloov chaw. Nyob rau hauv cov organic synthesis, cov dab muaj ib tug xov tooj ntawm cov nta uas yuav tsum tau muab sau tseg.

Ib tug ntau yam ntawm tshuaj phenomena. hloov cov tshuaj tiv thaiv

Tshuaj kev hloov uas txuam nrog rau transformation ntawm qhov teeb meem, ib tug xov tooj ntawm txawv nta. Tej zaum yuav sib txawv ua tau, thermal los; ib co dab yuav tag, nws los nyob rau hauv lwm yam tshuaj equilibrium. Modifying cov neeg ua hauj nws yog feem ntau nrog los ntawm kev ua los yog zuj zus lawm cov neeg kawm ntawv ntawm oxidation. Nyob rau hauv lub cais ntawm tshuaj phenomena nyob rau hauv lawv kawg tau ua kom lwm tus zoo thiab ntau sib txawv ntawm cov reactants los ntawm cov khoom. Tej yam no yuav ua tau distinguished 7 hom tshuaj haum, xws li hloov, txheej txhem raws li lub tswvyim: A-B-C A + C + B. Cov simplified cov ntaubntawv povthawj siv ntawm ib tug tag nrho cov chav kawm ntawv ntawm cov tshuaj phenomena muab ib lub tswv yim hais tias cov starting ntaub ntawv yog qhov thiaj li hu ua "attacker "particle substituent nyob rau hauv lub reagent atom, ion functional ib pawg. Cov hloov cov tshuaj tiv thaiv yog cov yam ntxwv ntawm nyeem thiab uas muaj ntxhiab hydrocarbons.

hloov cov tshuaj tiv thaiv yuav tshwm sim nyob rau hauv daim ntawv ntawm cov double-pauv: A-B-C + E C + A-B-E. Ib subspecies - xaav, e.g., tooj liab, hlau los ntawm ib tug tov ntawm tooj liab sulphate: CuSO ₄ + Fe = FeSO ₄ + Cu. Raws li cov "attacking" hais yuav ua atoms, ions los yog functional pawg

Homolytic hloov (radical, SR)

Thaum lub mechanism ntawm radical rupture covalent electron khub yog tshwm sim rau qhov sib txawv hais yuav tsum proportionally faib nruab nrab ntawm lub "thooj" ntawm lub molecule. Tsim kom muaj cov dawb radicals. Qhov no tsis ruaj tsis khov particle stabilization uas tshwm sim raws li ib tug tshwm sim ntawm tom ntej tshua. Piv txwv li, nyob rau hauv qhov kev npaj ntawm ethane los ntawm methane tsim dawb radicals muab kev koom tes nyob rau hauv lub hloov cov tshuaj tiv thaiv: CH ₄ CH ₃ • + • H; CH ₃ • + • CH ₃ → C2H5; H • + • H → H2. Homolytic daim ntawv cog lus cleavage nyob rau kev khiav hauj lwm mechanism ntawm hloov chaw yog cov yam ntxwv ntawm alkanes, cov tshuaj tiv thaiv yog ib cov saw cim. Lub methane H atoms tej zaum yuav successively hloov los ntawm chlorine. Piv rau hnov mob nrog bromine, iodine, tiam sis yog tsis tau mus ncaj qha mus hloov hydrogen alkanes, fluorine reacts heev kwm nrog lawv.

Heterolytic daim ntawv cog lus cleavage txoj kev

Thaum lub mechanism ntawm ion txaus hloov tshua, electrons yog unevenly faib cov hais tshiab khiv arisen. Lub losis tswvyim dabtsi khub ntawm electrons ncua tag nrho cov kev uas ib ntawm lub "thooj", feem ntau, rau kev sib txuas lus khub, lub sab uas tau offset tsis zoo ceev nyob rau hauv lub ncov qaumteb qabteb molecule. By hloov tshua muaj xws li cov tshuaj tiv thaiv ntawm tsim ntawm methyl cawv CH ₃ OH. Nyob rau hauv brommetane CH3Br kis molecule yog heterolytic cim, lub them hais yog ruaj khov. Methyl acquires ib tug zoo xwb, thiab bromo - tsis zoo: CH ₃ Br → CH ₃ ^{+ +} Br ^-; NaOH → Na ^{+ +} OH ^-; CH ₃ ^{+ +} OH ^- → CH ₃ OH; Na ^{+ +} Br ^- ↔ NaBr.

Electrophiles thiab nucleophiles

Hais tias tsis muaj electrons thiab yuav txais lawv, yog hu ua "electrophiles." Cov no yog cov pa roj carbon atoms sib raug zoo nrog halogens nyob rau hauv haloalkanes. Nucleophiles muaj siab electron ceev, lawv yog "cov neeg raug" ntawm ib khub electrons los ua ib tug covalent daim ntawv cog lus. Cov hloov tshua nplua nuj tsis zoo nqi yuav rov los nucleophiles electrophiles, sis tshaj ntawm electrons. Qhov no tshwm sim yog txuam nrog lub zog ntawm atoms los yog lwm tus - tawm hauv pab pawg neeg. Lwm ntau yam ntawm hloov chaw tshua - tua cov electrophile nucleophile. Tej thaum nyuaj rau paub qhov txawv nruab nrab ntawm ob dab, xa mus rau cov kev hloov ntawm ib tug los yog lwm hom, vim hais tias nws yog ib qhov nyuaj kom meej raws nraim li cas ntawm molecule - substrate, thiab cov uas - reagent. Feem ntau nyob rau hauv xws li mob, yam nram qab no yog xam tias yog:

• qhov xwm ntawm tus tawm hauv pab pawg neeg;
• lub reactivity ntawm lub nucleophile;
• qhov xwm ntawm tus kuab;
• lub alkyl feem ntawm cov qauv.

Nucleophilic hloov (SN)

Nyob rau hauv tus txheej txheem ntawm kev sis raug zoo nyob rau hauv cov organic molecule muaj tau ua polarization. Nyob rau hauv qhov sib npaug ntawm ib nrab los yog tsis zoo xwb yog qhia los ntawm tsab ntawv ntawm lub Greek cov tsiaj ntawv. Polarization kev sib txuas lus muab ib tug hais txog ntawm qhov xwm ntawm nws kev sib tawg thiab lub neej yav tom ntej tus cwj pwm ntawm "thooj" ntawm lub molecule. Piv txwv li, ib tug carbon atom nyob rau hauv iodomethane muaj ib tug ib nrab zoo xwb, nws yog ib qho electrophilic chaw. Nws attracts lub dipole ntawm cov dej, qhov chaw uas cov pa muaj ib tug dhau heev lawm ntawm electrons. Nyob rau hauv cov tshuaj tiv thaiv ntawm lub electrophile nrog ib tug nucleophile yog tsim methanol: CH ₃ Kuv + H ₂ O → CH ₃ OH + HI. nucleophilic hloov tshua muab qhov chaw nrog kev koom tes ntawm ib tug tsis zoo them ion los yog molecule muaj ib tug dawb electron khub, uas tsis koom nrog nyob rau hauv cov creation ntawm ib tug tshuaj daim ntawv cog lus. Active koom tes los ntawm iodomethane nyob rau hauv SN _{2-cov tshuaj tiv thaiv} vim nws qhib siab dawb paug rau nucleophilic nres thiab iodine muaj.

Electrophilic hloov (SE)

Cov organic molecule tej zaum yuav tam sim no nucleophilic chaw, uas yog yus muaj los ntawm ib tug dhau heev lawm ntawm electron ceev. Nws reacts nrog cov tsis muaj tsis zoo nqi electrophilic reagent. Tej hais yog atoms muaj free orbital molecule nrog feem ntawm txo electron ceev. Lub sodium formate carbon muaj xwb "-", yog reacted nrog ib tug zoo ib feem ntawm cov dej dipole - hydrogen: CH ₃ Na + H ₂ O → CH ₄ + NaOH. Cov khoom ntawm tshuaj tiv thaiv no, electrophilic hloov - methane. Thaum heterolytic tshua INTERACTIONS oppositely them chaw zov me nyuam ntawm cov organic molecules, uas muab lawv sib ze nrog ions nyob rau hauv inorganic tshuaj Science News for KIDS. Nws yuav tsum tsis tau overlooked hais tias cov conversion of organic tebchaw yog tsis tshua muaj nrog lub tsim ntawm cov cations thiab anions.

Unimolecular thiab bimolecular tshua

Lub nucleophilic hloov yog monomolecular (SN1). Los ntawm no mechanism, ib qho tseem ceeb cov khoom ntws hydrolysis ntawm organic synthesis - tertiary butyl chloride. Tus thawj theem yog qeeb, nws yog txuam nrog hnyav dissociation rau hauv carbonium ntawv thiab ib tug chloride anion. Qhov thib ob theem yog ib tug ceev cov tshuaj tiv thaiv no tshwm sim carbonium ion thiab dej. Cov kab zauv ntawm cov tshuaj tiv thaiv ntawm hloov chaw ntawm halogen nyob rau hauv lub alkane kom tau tej cov hydroxy thiab thawj cawv: (CH _{3) 3} C-Cl → (CH _{3) 3} C ^{+ +} Cl ^-; (CH _{3) 3} C ^{+ +} H ₂ O → (CH _{3) 3} C-OH ⁺ H +. Rau ib kauj ruam hydrolysis ntawm thawj thiab alkyl halides yus muaj los ntawm simultaneous kev puas tsuaj ntawm cov pa roj carbon vim halogen thiab tsim los ntawm khub C-OH. Qhov no nucleophilic bimolecular hloov mechanism (SN2).

Heterolytic mechanism ntawm hloov chaw

hloov mechanism yuav lub electron hloov lwm lub tsev, lub creation ntawm intermediate ceg. Cov tshuaj tiv thaiv hais ntau sai heev, qhov yooj yim dua nws yog rau cov raug intermediates rau nws. Feem ntau cov txheej txheem yuav nyob rau hauv ob peb qhia ib txhij. Qhov kom zoo dua feem ntau yog tau txais txoj kev nyob rau hauv uas tus hais yog siv, yuav tsum kawg expenditure ntawm lub zog rau nws tsim. Piv txwv li, lub xub ntiag ntawm ib tug muab ob npaug rau daim ntawv cog lus tsub kom qhov yuav ntawm ib tug allyl ntawv CH 2 = CH-CH ₂ ^+, piv rau lub _CH3 ⁺ ion. Yog vim li cas cov lus dag nyob rau hauv lub electron ceev ntawm lub ntau yam daim ntawv cog lus, uas muaj feem xyuam rau cov delocalization qhov zoo xwb, dispersed tshaj rau tag nrho cov qauv.

benzene hloov cov tshuaj tiv thaiv

Cov pab pawg neeg ntawm cov organic tebchaw, uas yog yus muaj los ntawm electrophilic hloov - arena. Benzene nplhaib - ib tug yooj yim kwv rau electrophilic nres. Cov txheej txheem yuav pib kev sib txuas lus nrog tus thib ob polarization reagent, li no txoj kev electrophile electron huab uas nyob ib sab lub benzene nplhaib. Cov no ib tug complex txoj kev hloov. Tseem ceeb sib txuas lus electrophilic hais nrog ib tug ntawm cov pa roj carbon atoms tsis tau, nws yog attracted rau tag nrho tsis zoo xwb "uas muaj ntxhiab rau" electrons. Nyob rau hauv lub thib peb kauj ruam ntawm tus txheej txheem electrophile thiab ib ntiv nplhaib carbon atom uake ib qho khub ntawm electrons (covalent daim ntawv cog lus). Tab sis nyob rau hauv cov ntaub ntawv no, yog kev puas tsuaj ntawm lub "uas muaj ntxhiab rau", uas yog disadvantageous nyob rau hauv cov nqe lus ntawm tsis tau zoo ib tug ruaj khov sustainable zog lub xeev. Muaj yog ib tug tshwm sim uas yuav hu tau ua "tso tawm ntawm ib tug proton." Nws yog phua tawm H ^+, recovering ib tug ruaj khov kev sib txuas lus system, raug arenes. Sab tshuaj muaj hydrogen ntawv ntawm ib tug benzene nplhaib thiab cov anion los ntawm tus thib ob reagent.

Piv txwv ntawm hloov chaw tshua ntawm organic Science News for KIDS

Rau alkanes tshwj xeeb tshaj yog raug hloov cov tshuaj tiv thaiv. Piv txwv ntawm electrophilic thiab nucleophilic tshua yuav ua rau cycloalkanes thiab arenes. Zoo ib yam li tshua nyob rau hauv lub lwg me me ntawm cov organic tshuaj uas nyob rau hauv ib txwm tej yam kev mob, tiam sis feem ntau - thiab los ntawm cua kub nyob rau hauv lub xub ntiag ntawm catalysts. By heev thiab zoo kawm dab xws li electrophilic uas muaj ntxhiab hloov chaw. Qhov tseem ceeb tshaj cov tshuaj tiv thaiv ntawm no hom:

1. Nitration ntawm benzene nrog nitric acid nyob rau hauv lub xub ntiag ntawm H ₂ li ₄ - raws li cov tswvyim: C ₆ H ₆ → C ₆ H ₅ -Tsis _2.
2. Lub catalytic halogenation ntawm benzene, tshwj xeeb tshaj yog chlorination, los ntawm cov kab zauv: C ₆ H ₆ + Cl ₂ → C ₆ H ₅ Cl + HCl.
3. Aromatic sulfonation ntawm benzene proceeds nrog "fuming" sulfuric acid, benzenesulfonic acid yog tsim.
4. Alkylation - kev hloov ntawm lub hydrogen atom los ntawm cov benzene nplhaib rau alkyl.
5. Acylation - lub tsim ntawm ketones.
6. Formylation - hloov ib tug hydrogen rau ib pab pawg neeg Cho thiab tsim los ntawm aldehydes.

By hloov tshua muaj xws li cov tshuaj tiv thaiv nyob rau hauv alkanes thiab cycloalkanes, nyob rau lub halogens tua muaj C-H daim ntawv cog lus. Derivatization tej zaum yuav txuam nrog kev hloov ntawm ib tug, ob tug los yog tag nrho ntawm cov hydrogen atoms nyeem hydrocarbons thiab cycloparaffins. Muaj ntau ntawm galogenoalkanov ntawm tsawg molecular yuag yog siv nyob rau hauv qhuav ntawm ntau yam teej tug mus rau txawv cov chav kawm ntawv. Cov successes tiav nyob rau hauv txoj kev tshawb no ntawm mechanisms ntawm hloov chaw tshua, muab ib tug haib impetus mus rau lub kev loj hlob ntawm syntheses rau lub hauv paus ntawm alkanes, cyclo-theem thiab halogenated hydrocarbons.