Acetals muaj ob -OR pawg, ib pawg -R thiab ib -H atom. Hauv hemiacetals, ib qho ntawm -OR pawg hauv acetals yog hloov los ntawm ib pawg -OH. Qhov no yog qhov sib txawv tseem ceeb ntawm acetal thiab hemiacetal.
Acetals thiab hemiacetals yog ob pawg ua haujlwm uas feem ntau pom hauv cov khoom ntuj. Hemiacetal yog ib qho tshuaj nruab nrab ntawm cov tshuaj sib xyaw ua ke tsim thaum lub sijhawm tshuaj lom neeg ntawm kev tsim acetal. Yog li ntawd, ob pawg no muaj qhov sib txawv me ntsis hauv lawv cov qauv tshuaj. Nyob rau hauv kev nthuav dav, lub hauv paus carbon atom nyob rau hauv ob qho tib si ntawm cov tebchaw yog ib tug sp3-C atom bonded rau plaub daim ntawv cog lus, thiab tawm ntawm plaub daim ntawv cog lus, tsuas yog ib tug bonding hom sib txawv.
Acetal yog dab tsi?
Acetal yog ib pawg ua haujlwm uas lub hauv paus carbon atom muaj plaub daim ntawv cog lus; -OR1, -OR2, -R3 thiab H (qhov twg R 1, R2 thiab R3 pawg yog cov khoom tawg yooj yim). Ob pawg -OR tuaj yeem sib npaug rau ib leeg (symmetric acetals) lossis sib txawv (sib xyaw acetal).
Daim duab 1: Acetal
Lub hauv paus carbon atom yog hais tias yuav saturated vim nws muaj plaub daim ntawv cog lus thiab qhov no muab lub hauv paus carbon atom ib tug tetrahedral geometry. Acetals tuaj yeem tsim los ntawm aldehydes. Kev tsim ntawm acetal tuaj yeem tshwm sim thaum pawg hydroxyl ntawm hemiacetal ua protonated kom poob dej molecule. Qhov tshwm sim carbocation yog sai heev los ntawm ib tug cawv molecule. Thaum lub sij hawm kawg, kev tsim acetal tiav tom qab tau txais ib qho proton los ntawm cov cawv. Cov txheej txheem rau kev tsim cov acetals tuaj yeem piav qhia raws li hauv qab no.
Daim duab 2: Tsim cov Acetals
Ntxiv rau, acetals yog siv los tiv thaiv pawg carbonyl hauv cov organic synthesis vim lawv ruaj khov nrog ntau oxidizing thiab txo cov neeg ua haujlwm thiab hauv hydrolysis hauv nruab nrab nruab nrab.
Examples
Qee yam piv txwv ntawm cov tshuaj sib xyaw uas muaj acetal functional pawg muaj raws li hauv qab no.
- YDimethoxymethane: ib qho hnyav
- Dioxolane
- Metaldehyde
- Paraldehyde
- Feem ntau glycosidic bonds hauv carbohydrates thiab lwm yam polysaccharides yog acetal linkages.
- Cellulose yog ib qho piv txwv ntawm ib qho polyacetal.
- Polyoxymethylene (POM): formaldehyde polymer uas yog siv los ua yas.
- 1, 1-Diethoxyethane (acetaldehyde diethyl acetal), yog tus neeg sawv cev tseem ceeb hauv cov dej haus distilled.
Hemiacetal yog dab tsi?
Hemiacetals yog muab los ntawm aldehydes thiab lo lus Hemiacetal los ntawm Greek lo lus "hemi" txhais tau tias "ib nrab".
Daim duab 3: Hemiacetal
Hemiacetals tuaj yeem tsim los siv ntau txoj hauv kev; los ntawm nucleophilic ntxiv ntawm cawv rau ib qho aldehyde, los ntawm nucleophilic ntxiv ntawm cawv rau lub resonance stabilized hemiacetal cation thiab los ntawm ib nrab hydrolysis ntawm acetal.
Daim duab 4: Kev tsim ntawm Hemiacetal
Lub ntsiab yam ntxwv ntawm lub hemiacetal molecule yog muaj lub hauv paus carbon atom nrog plaub sib txawv bonds; -OR1 pab pawg, -R2 pab pawg, -H pab pawg thiab -OH pab pawg.
Examples
Feem ntau ntawm cov hemiacetals pom muaj ntau pawg ua haujlwm hauv cov khoom ntuj. Qee qhov piv txwv yog;
- YGlucose
- Mycorrhizin A
- Thromboxane B2
Qhov txawv ntawm Acetal thiab Hemiacetal yog dab tsi?
Acetal ua haujlwm pab pawg muaj sp3 hybridized carbon atom uas yog sib koom ua ke rau ob pawg -OR, hydrogen atom, thiab -R pawg. Nyob rau hauv sib piv, lub hauv paus atom ntawm hemiacetals muaj ib tug sp3-C atom bonded rau plaub pawg tshuaj sib txawv; lawv yog -OR, -R, -OH thiab -H.
Acetals yog tshuaj ruaj khov piv rau hemiacetals. Txawm li cas los xij, acetals tau yooj yim hydrolyze rov qab rau lawv niam lawv txiv cawv thiab cov carbonyl compound nyob rau hauv muaj cov aqueous acids. Feem ntau, peb feem ntau xav txog hemiacetals ua cov tshuaj tsis ruaj khov, yog li ntawd, lawv nyiam tsim cov qauv nplhaib los txhawb kev ruaj ntseg. Nyob rau hauv cov ntaub ntawv no, tsim 5 los yog 6- membered rings yog ua tau, thiab qhov no tshwm sim los ntawm cov tshuaj tiv thaiv ntawm pawg -OH nrog ib tug carbonyl pawg. Ob qho piv txwv ntawm cyclic hemiacetals yog qabzib thiab aldose.
Summary – Acetal vs Hemiacetal
Acetals muaj ob -OR pawg, ib pawg -R thiab ib -H atom. Hauv hemiacetals, ib qho ntawm -OR pawg hauv acetals yog hloov los ntawm ib pawg -OH. Qhov no yog qhov sib txawv ntawm acetal thiab hemiacetal.
