Yuav ua li cas yog raug tshuaj rau alkanes

Txhua chav kawm ntawv ntawm cov tshuaj lub tebchaw yuav muaj zog vim lawv hluav taws xob qauv. Rau alkanes raug hloov cov tshuaj tiv thaiv, cleavage los yog molecular oxidation. Tag nrho cov tshuaj dab muaj lawv tus kheej kev khiav, uas yuav tsum tau ntxiv los sib tham.

Yuav ua li cas yog alkanes

Qhov no nyeem hydrocarbon tebchaw, uas yog lub npe hu ua paraffin. Cov molecules muaj tsuas carbon thiab hydrogen atoms, yog linear los yog branched acyclic saw nyob rau hauv uas muaj yog tsuas muaj ib zaug xwb compound. Muab cov yam ntxwv ntawm cov chav kawm ntawv, koj yuav xam li cas cov tshuaj tiv thaiv cov yam ntxwv ntawm alkanes. Lawv ua li tus qauv rau tag nrho cov chav kawm ntawv: H _{2n + 2} C _n.

tshuaj qauv

Paraffin molecule muaj carbon atoms seeb sp ³ hybridization. Lawv tag nrho cov plaub valence orbitals muaj tib lub zoo, lub zog thiab kev taw qhia nyob rau hauv qhov chaw. Qhov luaj li cas ntawm lub kaum sab xis ntawm lub zog theem ntawm 109 ° thiab 28 '.

Qhov kuaj pom ntawm ib bonds nyob rau hauv molecules txiav txim seb tshua yog cov yam ntxwv ntawm alkanes. Lawv muaj σ-compound. Kev sib txuas lus nruab nrab carbons yog nonpolar thiab weakly polarizable, nws yog me ntsis ntev tshaj li C-H. Tsis tas li ntawd, lub electron ceev ntawm ib tug ua haujlwm rau ib tug carbon atom yog lub feem ntau electronegative. Cov uas ua compound yog yus muaj los ntawm C-H tsawg polarity.

hloov cov tshuaj tiv thaiv

Tshuaj hauv chav kawm ntawv paraffins muaj ib tug uas tsis muaj tshuaj lom neeg kev ua si. Qhov no yuav ua tau piav los ntawm lub dag lub zog ntawm bonds ntawm C-C thiab C-H, uas yog ib qho nyuaj mus ua txhaum vim hais tias ntawm qhov uas tsis yog-polarity. Lub hauv paus ntawm lawv kev puas tsuaj yog homolytic mechanism, nyob rau lub free radical hom muab kev koom tes. Uas yog vim li cas alkanes yog yus muaj los ntawm ib tug hloov cov tshuaj tiv thaiv. Tej yam yuav tau mus nrog cov dej lwg me me los yog ions ntawm tus nqi muaj.

Lawv rank free radical hloov nyob rau hauv uas lub hydrogen atoms yog hloov los ntawm halogen ntsiab los yog lwm yam active pab pawg neeg. Cov tshua muaj xws li dab hais txog halogenation, sulfochlorination thiab nitration. Cov ua rau qhov kev npaj ntawm alkane derivatives. Lwm hloov tshua ntawm ib tug dawb radical mechanism yog lub ntsiab hom peb theem:

1. Txheej txheem yuav pib nrog ib nucleation pib los yog tej saw, nyob rau hauv uas dawb radicals yog tsim. Lub catalysts yog qhov chaw ntawm ultraviolet lub teeb thiab cua sov.
2. Ces npaj saw nyob rau hauv uas successive active hais kwv sis raug zoo nrog tsaug zog molecules. Yog lawv hloov dua siab tshiab rau hauv molecules thiab radicals, ntsig txog.
3. Cov kauj ruam kawg yuav ua txhaum lub saw. Muaj recombination los yog disappearance ntawm lub active hais. Yog li haujlwm txoj kev loj hlob ntawm ib cov saw tshuaj tiv thaiv.

Tus txheej txheem ntawm halogenation

Nws yog raws li nyob rau hauv lub mechanism ntawm radical hom. Alkane halogenation cov tshuaj tiv thaiv yuav siv sij hawm qhov chaw los ntawm irradiation nrog ultraviolet lub teeb thiab cua sov ntawm ib tug sib tov ntawm halogens thiab hydrocarbons.

Tag nrho cov ua sawv ntawm txoj kev muaj kev kawm rau txoj cai uas tau teev Markovnikov. Nws hais tias undergoes hloov los ntawm halogen, tshwj xeeb tshaj yog hydrogen, uas belongs rau lub hydrogenated carbon. Halogenation yuav siv sij hawm qhov chaw nyob rau hauv cov nram no ib theem zuj zus: los ntawm ib tug thawj mus rau ib tug tertiary carbon atom.

Cov txheej txheem yuav siv sij hawm qhov chaw zoo nyob rau hauv alkane molecules nrog qhov ntev ntsiab hydrocarbon saw. Qhov no yog vim lub thawj ntawm ionizing zog nyob rau hauv no kev taw qhia, cov tshuaj yeeb dej caw yooj yim cleaved electron.

Ib qho piv txwv yog lub chlorination ntawm methane molecules. Qhov kev txiav txim ntawm ultraviolet tawg ua rau ib tug splitting tshuaj radical hom uas nqa tawm ib qho kev tua nyob rau lub alkane. Sib cais tshwm sim thiab tsim los ntawm atomic hydrogen H ₃ C · los yog ib tug methyl radical. Xws li ib tug particle, nyob rau hauv lem, tua cov molecular tshuaj, ua rau kev puas tsuaj ntawm nws cov qauv thiab tsim ntawm ib tug tshiab tshuaj.

Nyob rau txhua theem lub hloov txheej txheem yog nqa tawm tsuas yog ib hydrogen atom. Lub halogenation cov tshuaj tiv thaiv ntawm alkanes ua rau lub tsheb txhob sibtsoo tsim ntawm hlormetanovoy, dichloromethane, thiab trihlormetanovoy tetrahlormetanovoy molecule.

Schematically, cov txheej txheem raws li nram no:

H ₄ C + Cl: Cl → H ₃ CCl + HCl,

H ₃ CCl + Cl: Cl → H ₂ CCl ₂ + HCl,

H ₂ CCl ₂ + Cl: Cl → HCCl ₃ + HCl,

HCCl ₃ + Cl: Cl → CCl ₄ + HCl.

Nyob rau hauv sib piv rau lub chlorination ntawm methane molecules nqa xws li ib tug txheej txheem nrog rau lwm cov alkanes yus tau tshuaj muaj hydrogen hloov tsis yog ib tug carbon atom, thiab nyob rau hauv ob peb tug. Lawv ntau piv txuam nrog kub ntsuas. Nyob rau hauv txias tej yam kev mob, ib tug txo nyob rau hauv tus nqi ntawm tsim ntawm derivatives nrog tertiary, nrab thiab thawj qauv.

Nrog ua kub lub hom phiaj kev ceev ntawm tsim ntawm xws tebchaw yog leveled. Nyob rau hauv lub halogenation txheej txheem muaj tus ntawm qhov zoo li qub zoo tshaj uas qhia ib tug txawv ntau yam ntawm kev sib tsoo ntawm cov radical nrog cov pa roj carbon atom.

Txheej txheem halogenation nrog iodine tsis tshwm sim nyob rau hauv ib txwm tej yam kev mob. Nws yog tsim nyog los tsim tej yam kev mob tshwj xeeb. Thaum raug rau methane tshwm sim raws li halogen tshwm sim hydrogen iodide. Nws muaj ib cov nyhuv rau methyl iodide raws li ib tug tshwm sim sawv tawm thawj zaug reactants methane thiab iodine. Xws li ib tug tshuaj tiv thaiv yog pom tias yuav tau reversible.

Wurtz cov tshuaj tiv thaiv ntawm alkanes

Nws yog ib txoj kev rau muab hydrocarbons nrog lub uas symmetrical qauv. Raws li cov reactants yog siv sodium hlau, alkyl bromides los yog alkyl chlorides. Nrog lawv sib tham npaj sodium halide thiab muaj zog hydrocarbon saw uas yog lub sum ntawm ob hydrocarbon radicals. Schematically, lub synthesis yog raws li nram no: R-Cl + Cl-R + 2Na → R-R + 2NaCl.

Wurtz cov tshuaj tiv thaiv ntawm alkanes no tsuas tau yog hais tias tus halogens nyob rau hauv lawv cov molecules yog nyob rau thawj carbon atom. E.g., CH ₃ -CH ₂ -CH ₂ Br.

Yog hais tias thaum lub sij hawm ua si ntawm galogenuglevodorododnaya sib tov ntawm ob lub tebchaw, nyob rau hauv lub hws ntawm peb sib txawv chains tsim khoom. Ib qho piv txwv ntawm no cov tshuaj tiv thaiv yuav ua raws li sodium alkane sis raug zoo nrog chloromethanes thiab hloretanom. Lub tso zis yog ib tug sib tov muaj butane, hluav taws roj zeb thiab ethane.

Dhau li sodium, tau siv lwm yam alkali hlau, uas muaj xws li lithium los yog poov tshuaj.

txheej txheem sulfochlorination

Nws tseem hu ua lub Reed cov tshuaj tiv thaiv. Nws sau nyob rau hauv lub hauv paus ntsiab lus ntawm free hloov. Qhov no hom ntawm cov tshuaj tiv thaiv yog ntse alkanes rau qhov kev txiav txim ntawm ib tug sib tov ntawm cov leej faj dioxide thiab molecular tshuaj nyob rau hauv lub xub ntiag ntawm ultraviolet tawg.

Cov txheej txheem yuav pib nrog qhov pib ntawm lub saw mechanism, nyob rau cov tshuaj uas tau los ntawm lub ob radicals. Ib nres alkane uas muab sawv mus rau ib tug alkyl hais thiab molecules ntawm hydrogen chloride. Los ntawm hydrocarbon radical uas txuas mus rau tsim cov leej faj dioxide complex hais. Yuav kom tswj capture tshwm sim ib cov tshuaj atom los ntawm lwm molecule. Qhov kawg cov ntaub ntawv uas yog ib tug alkane sulfonyl chloride, nws yog siv nyob rau hauv lub synthesis ntawm nto-lub tebchaw.

Schematically, cov txheej txheem zoo li no:

CLCL → ^HV ∙ Cl + ∙ Cl,

HR + ∙ Cl → R ∙ + HCl,

R ∙ + OSO → ∙ RSO _2,

∙ RSO ₂ + ClCl → RSO ₂ Cl + ∙ Cl.

Cov dab txuam nrog nitration

Alkanes hnov mob nrog nitric acid nyob rau hauv ib tug tov 10% thiab nrog rau cov tetravalent nitrogen oxide nyob rau hauv ib tug gaseous lub xeev. Tej yam kev mob ntawm nws tshwm sim yog siab qhov tseem ceeb ntawm kub (txog 140 ° C) thiab tsis tshua muaj siab qhov tseem ceeb. Thaum cov qhov tso zis ua nitroalkanes.

Tus txheej txheem ntawm dawb-radical hom hu ua tom qab tus paub txog Konovalov, qhib nitration synthesis: CH ₄ + HNO ₃ → CH ₃ TSIS MUAJ ₂ + H ₂ O.

Lub mechanism ntawm cleavage

Rau cov raug alkane dehydrogenation thiab cracking. Methane molecule undergoes ib tug ua tiav thermal decomposition.

Cov yooj yim mechanism ntawm qhov saum toj tshua yog lub cleavage ntawm atoms ntawm alkanes.

dehydrogenation txheej txheem

Thaum nkauj nraug lub hydrogen atoms ntawm cov pa roj carbon lub cev pob txha ntawm paraffins, tsuas yog methane yog tau unsaturated tebchaw. Tej tshuaj tshua ntawm alkanes kuaj thaum muaj kev kub kub (400 rau 600 ° C) thiab nyob rau hauv qhov kev txiav txim accelerators li platinum, npib tsib xee, chromium oxides thiab txhuas.

Yog hais tias koom nyob rau hauv cov tshuaj tiv thaiv ntawm ethane los yog hluav taws roj zeb molecules, ces nws cov khoom yuav ethene los yog propene nrog ib tug muab ob npaug rau daim ntawv cog lus.

Lub dehydrogenation ntawm cov plaub los yog tsib-carbon lub cev pob txha tau diene compound. Los ntawm tsim butane-1,3 butadiene thiab 1,2-butadiene.

Yog hais tias tam sim no nyob rau hauv cov tshuaj tiv thaiv tshuaj nrog 6 los yog ntau tshaj carbon atoms, cov benzene yog tsim. Nws muaj ib tug uas muaj ntxhiab nplhaib nrog peb ob bonds.

Cov txheej txheem txuam nrog decomposition

Nyob rau hauv high school kub tshuaj tiv thaiv ntawm alkanes yuav kis tau nrog ib tug kis carbon bonds thiab tsim ntawm active hom radical hom. Tej dab raug xa mus rau raws li cracking los yog pyrolysis.

Cua sov lub reactants rau kub siab tshaj 500 ° C, tau nyob rau hauv lub decomposition ntawm lub lwg me me nyob rau hauv uas yog tsim nyob rau txoj mixtures ntawm alkyl-hom radicals.

Nqa tawm nyob rau hauv muaj zog cua sov ntawm lub pyrolysis ntawm alkanes nrog ib tug carbon saw ntev vim tau noo thiab unsaturated tebchaw. Nws yog hu ua thermal cracking. Qhov no tus txheej txheem no siv kom txog thaum lub nruab nrab-xyoo pua 20th.

Lub drawback yog kom tau hydrocarbons nrog ib tug tsawg octane tooj (tsawg tshaj li 65), ces nws twb hloov ntes catalyst. Cov txheej txheem yuav siv sij hawm qhov chaw nyob rau kub uas yog hauv qab no 440 ° C, thiab pressures ntawm tsawg tshaj li 15 atmospheres, nyob rau hauv lub xub ntiag ntawm ib aluminosilicate tsuj roj tso tawm alkanes muaj ib tug branched qauv. Ib qho piv txwv yog lub pyrolysis ntawm methane: 2CH ₄ → ^{t °} C ₂ H ₂ + 3H _2. Cov tsim acetylene thiab molecular hydrogen thaum lub sij hawm cov tshuaj tiv thaiv.

Lub molecule tej zaum yuav raug mus rau methane hloov dua siab tshiab. Yuav kom qhov no cov tshuaj tiv thaiv yuav tsum tau dej thiab ib tug npib tsib xee catalyst. Lub tso zis yog ib tug sib tov ntawm cov pa roj carbon monoxide thiab hydrogen.

oxidation dab

Cov tshuaj tshua uas yog raug alkane txuam nrog electron tej yam.

Muaj yog auto-oxidation ntawm paraffins. Nws yuav ib tug dawb radical mechanism ntawm oxidation ntawm nyeem hydrocarbons. Thaum lub sij hawm cov tshuaj tiv thaiv, kua theem alkane hydroperoxide tau. Chiv paraffin molecule reacts nrog rau oxygen hauv cov faib active radicals. Tom ntej no, alkyl particle ua num ua ke lwm molecule O _2, tau ∙ ROO. Txij li thaum lub peroxy radical ntawm ib tug fatty acid yog hu alkane molecule, thiab ces tso tawm hydroperoxide. Ib qho piv txwv yog lub autooxidation ntawm ethane:

C ₂ H ₆ + O ₂ → ∙ C ₂ H ₅ + hoo ∙,

∙ C ₅ H ₂ + O ₂ → ∙ OOC ₂ H _5,

∙ OOC ₂ H ₅ + C ₂ H ₆ → HOOC ₂ H ₅ + ∙ C ₂ H _5.

Rau alkane tsiag ntawv los ntawm cov tshuaj tiv thaiv ntawm combustion uas yog mas tshuaj zog, nyob rau hauv kev txiav txim nyob tus yeees ntawm ib tug roj. Lawv yog cov oxidative nyob rau hauv cov xwm nrog cov emission ntawm tshav kub: 2C ₂ H ₆ + 7O ₂ → 4CO ₂ + 6H ₂ O.

Yog hais tias tus txheej txheem yog cai nyob rau hauv ib tug me me npaum li cas ntawm cov pa, kawg cov khoom yuav ua tau ib tug divalent carbon los yog cov pa roj carbon monoxide, uas yog txiav txim los ntawm lub concentration ntawm O _2.

Nyob rau hauv lub oxidation ntawm alkanes nyob rau hauv tus ntawm catalytic tshuaj thiab rhuab rau 200 ° C yog tau cawv molecule, aldehyde los yog carboxylic acid.

QAUV ethane:

C ₂ H ₆ + O ₂ → C ₂ H ₅ OH (ethanol),

C ₂ H ₆ + O ₂ → CH ₃ Cho + H ₂ O (ethanal thiab dej)

2C ₂ H ₆ + 3O ₂ → 2CH ₃ COOH + 2H ₂ O (ethanoic acid thiab dej).

Alkanes yuav oxidized nyob rau hauv qhov kev txiav txim ntawm cyclic peroxides trinomial. Cov no muaj xws dimethyl dioxirane. Cov no cov oxidation uas paraffins cawv molecule.

Cov neeg sawv cev paraffins tsis teb KMnO ₄ los yog poov tshuaj permanganate, raws li zoo raws li bromine dej.

isomerization

Nyob rau alkanes yus hloov hom tshuaj tiv thaiv nrog ib tug electrophilic mechanism. Qhov no yog isomerization ntawm cov pa roj carbon saw. Catalyzes no lub txhuas chloride, uas yog reacted nrog ib tug nyeem paraffin. Ib qho piv txwv yog lub isomerization ntawm butane molecule, uas yog 2-methylpropane: C ₄ H ₁₀ → C ₃ H ₇ CH _3.

txheej txheem flavoring

Nyeem tshuaj nyob rau hauv uas lub ntsiab carbon saw muaj rau los yog ntau tshaj carbon atoms, muaj peev xwm ntawm kev dehydrocyclization. Rau hauv lub luv luv molecules yog tsis yam ntxwv ntawm tshuaj tiv thaiv no. Cov no yeej ib txwm ib tug rau-membered nplhaib raws li cyclohexane thiab derivatives thereof.

Nyob rau hauv lub xub ntiag ntawm cov tshuaj tiv thaiv accelerators, thiab dhau qhov ntxiv dehydrogenation ntawm hloov dua siab tshiab rau hauv ib tug ntau ruaj khov benzene nplhaib. Nws tshwm sim converting acyclic hydrocarbons rau aromatics los yog arena. Ib qho piv txwv yog lub dehydrocyclization ntawm hexane:

H ₃ C-CH ₂ - CH ₂ - CH ₂ - CH ₂ -CH ₃ → C ₆ H ₁₂ (cyclohexane)

C ₆ H ₁₂ → C ₆ H ₆ + 3H ₂ (benzene).