Qhov Sib txawv ntawm SN1 thiab SN2 Cov Lus Teb

2024 Tus sau: Alex Aldridge | [email protected]. Kawg hloov kho: 2023-12-17 13:40

Qhov Tseem Ceeb Qhov txawv - SN1 vs SN2 Cov Lus Teb

Cov tshuaj tiv thaiv SN1 thiab SN2 yog cov tshuaj tiv thaiv nucleophilic hloov pauv thiab feem ntau pom muaj nyob hauv Organic Chemistry. Ob lub cim SN1 thiab SN2 xa mus rau ob lub tshuab ua haujlwm. Lub cim SN sawv cev rau "kev hloov pauv nucleophilic". Txawm hais tias ob qho tib si SN1 thiab SN2 nyob hauv tib pawg, lawv muaj ntau qhov sib txawv nrog rau cov tshuaj tiv thaiv, nucleophiles thiab cov kuab tshuaj tau koom nrog cov tshuaj tiv thaiv, thiab cov yam ntxwv cuam tshuam rau tus nqi txiav txim siab theem. Qhov sib txawv tseem ceeb ntawm SN1 thiab SN2 cov tshuaj tiv thaiv yog SN₁ cov tshuaj tiv thaiv muaj ob peb kauj ruam whereas SN_{2 kev tawm tsam tsuas muaj ib kauj ruam xwb.}

SN1 Kev Pom Zoo yog dab tsi?

Nyob rau hauv SN1 cov tshuaj tiv thaiv, 1 qhia tias tus nqi txiav txim cov kauj ruam yog unimolecular. Yog li, cov tshuaj tiv thaiv muaj qhov kev txiav txim thawj zaug ntawm electrophile thiab xoom xaj dependence rau nucleophile. Ib qho carbocation yog tsim los ua ib qho nruab nrab hauv cov tshuaj tiv thaiv no thiab cov tshuaj tiv thaiv no feem ntau tshwm sim hauv cov dej cawv theem nrab thiab qib siab. SN1 kev tshwm sim muaj peb kauj ruam.

1. Tsim cov carbocation los ntawm kev tshem tawm pawg tawm.



2. Cov tshuaj tiv thaiv ntawm carbocation thiab nucleophile (Nucleophilic nres).



3. Qhov no tshwm sim tsuas yog thaum cov nucleophile yog ib qho nruab nrab (cov kuab tshuaj).

SN2 Cov Lus Teb yog dab tsi?

Nyob rau hauv SN2 kev tshwm sim, ib daim ntawv cog lus tau tawg, thiab ib daim ntawv cog lus tau tsim ib txhij. Hauv lwm lo lus, qhov no suav nrog kev hloov pauv ntawm pawg tawm los ntawm nucleophile. Cov tshuaj tiv thaiv no tshwm sim tau zoo heev hauv methyl thiab thawj alkyl halides thaum qeeb qeeb hauv tertiary alkyl halides txij li qhov kev tawm tsam rov qab raug thaiv los ntawm pawg loj.

Cov txheej txheem dav dav rau SN2 cov tshuaj tiv thaiv tuaj yeem piav qhia raws li hauv qab no.

Qhov txawv ntawm SN1 thiab SN2 Cov Lus Teb yog dab tsi?

Cov yam ntxwv ntawm SN1 thiab SN2 Reactions:

Mechanism:

SN1 Kev tshwm sim: SN _{1 kev tshwm sim muaj ob peb kauj ruam; Nws pib nrog kev tshem tawm ntawm pawg tawm, ua rau carbocation thiab tom qab ntawd kev tawm tsam los ntawm nucleophile.}

SN2 Cov Lus Teb: SN _{2cov tshuaj tiv thaiv yog ib kauj ruam cov tshuaj tiv thaiv uas ob qho tib si nucleophile thiab substrate koom nrog hauv tus nqi txiav txim siab theem. Yog li ntawd, qhov concentration ntawm cov substrate thiab cov nucleophile yuav cuam tshuam rau tus nqi txiav txim kauj ruam.}

Txoj kev cuam tshuam ntawm cov tshuaj tiv thaiv:

SN1 Cov Lus Teb: Thawj kauj ruam ntawm SN1 cov tshuaj tiv thaiv yog tshem tawm cov pab pawg tawm mus muab cov carbocation. Tus nqi ntawm cov tshuaj tiv thaiv yog proportional rau stability ntawm carbocation. Yog li, kev tsim cov carbocation yog qhov teeb meem loj tshaj plaws hauv SN1 cov tshuaj tiv thaiv. Kev ruaj ntseg ntawm carbocation nce nrog tus naj npawb ntawm cov hloov pauv thiab cov resonance. Tertiary carbocations yog qhov ruaj khov tshaj plaws thiab thawj carbocations yog qhov tsawg tshaj plaws ruaj khov (tertiary > theem nrab > thawj).

SN2 Cov Lus Teb: Steric hindrance yog qhov teeb meem hauv SN_{2 kev tshwm sim txij li thaum nws pib los ntawm kev tawm tsam rov qab. Qhov no tsuas yog tshwm sim yog tias qhov khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob khoob Thaum ntau pab pawg txuas nrog rau pawg tawm, nws ua rau cov tshuaj tiv thaiv qeeb. Yog li cov tshuaj tiv thaiv sai tshaj plaws tshwm sim hauv kev tsim cov thawj carbocations qhov qeeb tshaj plaws yog nyob rau hauv tertiary carbocations (thawj-ces tshaj > theem nrab > tertiary -slowest).}

Nucleophile:

SN1 Cov Lus Teb: SN ₁cov tshuaj tiv thaiv xav tau cov nucleophiles tsis muaj zog; lawv yog cov kuab tshuaj nruab nrab xws li CH₃OH, H₂O, thiab CH₃CH 2_OH.

SN2 Cov Lus Teb: SN ₂ cov tshuaj tiv thaiv xav tau cov nucleophiles muaj zog. Hauv lwm lo lus, lawv raug nqi tsis zoo nucleophiles xws liCH₃O^–, CN^–, RS ^–, N₃^– thiab HO^–.

Solvent:

SN1 Cov Lus Teb: SN1 cov tshuaj tiv thaiv yog nyiam los ntawm cov kuab tshuaj polar protic. Piv txwv yog dej, cawv, thiab carboxylic acids. Lawv tuaj yeem ua raws li cov nucleophiles rau cov tshuaj tiv thaiv.

SN2 Cov Lus Teb: SN2 cov tshuaj tiv thaiv ua tau zoo hauv cov kuab tshuaj polar aprotic xws li acetone, DMSO, thiab acetonitrile.

Definition:

Nucleophile: ib hom tshuaj uas pub ib khub electron rau ib qho electrophile los tsim ib daim ntawv cog lus tshuaj nyob rau hauv kev sib raug zoo.

Electrophile: ib qho reagent attracted rau electrons, lawv yog zoo them los yog nruab nrab hom uas tsis muaj orbitals uas yog attracted rau ib tug electron nplua nuj centre.