Nucleophilicity vs Basicity
Acids thiab hauv paus yog ob lub ntsiab lus tseem ceeb hauv chemistry. Lawv muaj contradictory khoom. Nucleophile yog ib lo lus, uas yog siv ntau tshaj nyob rau hauv cov organic chemistry, los piav txog cov tshuaj tiv thaiv mechanisms thiab cov nqi. Raws li txoj cai, tsis muaj qhov sib txawv ntawm cov hauv paus thiab nucleophiles, tab sis ua haujlwm lawv ua haujlwm sib txawv.
Nucleophilicity yog dab tsi?
Nucleophilicity txhais tau tias muaj peev xwm ntawm ib hom los ua tus nucleophile. Ib qho nucleophile tuaj yeem yog ib qho tsis zoo ion lossis ib qho nruab nrab molecule uas muaj tsawg kawg yog ib qho tsis sib koom ua ke. Nucleophile yog ib yam khoom uas muaj electropositive heev, yog li ntawd, nyiam cuam tshuam nrog cov chaw zoo. Nws tuaj yeem pib cov tshuaj tiv thaiv siv ib leeg electron khub. Piv txwv li, thaum ib tug nucleophile reacts nrog ib tug alkyl halide, ib leeg khub ntawm nucleophile tawm tsam cov pa roj carbon atom uas bears lub halogen. Cov pa roj carbon atom no yog ib feem zoo them vim qhov sib txawv ntawm electronegativity ntawm nws thiab halogen atom. Tom qab cov nucleophile txuas rau cov pa roj carbon, cov halogen tawm. Cov tshuaj tiv thaiv no yog hu ua nucleophilic hloov pauv cov tshuaj tiv thaiv. Muaj lwm hom kev tshwm sim pib los ntawm nucleophiles, hu ua nucleophilic tshem tawm cov tshuaj tiv thaiv. Nucleophilicity qhia txog cov tshuaj tiv thaiv mechanisms; yog li, nws yog ib qho qhia txog cov tshuaj tiv thaiv. Piv txwv li, yog tias cov nucleophilicity siab, ces ib qho tshuaj tiv thaiv tuaj yeem ceev ceev, thiab yog tias cov nucleophilicity tsawg, cov tshuaj tiv thaiv qeeb. Txij li thaum nucleophiles pub electrons, raws li Lewis txhais, lawv yog cov hauv paus.
Dab tsi yog qhov yooj yim?
Basicity yog lub peev xwm los ua lub hauv paus. Lub hauv paus tau txhais nyob rau hauv ntau txoj kev los ntawm ntau tus kws tshawb fawb. Arrhenius txhais lub hauv paus ua ib yam khoom uas pub OH– ions rau cov tshuaj. Bronsted- Lowry txhais lub hauv paus ua ib yam khoom uas tuaj yeem txais tau ib qho proton. Raws li Lewis, txhua tus neeg pub khoom siv hluav taws xob yog lub hauv paus. Raws li Arrhenius txhais, ib qho chaw yuav tsum muaj hydroxide anion thiab muaj peev xwm pub dawb los ua hydroxide ion los ua lub hauv paus. Tab sis raws li Lewis thiab Bronsted- Lowry, tuaj yeem muaj cov molecules, uas tsis muaj hydroxides, tab sis tuaj yeem ua lub hauv paus. Piv txwv li, NH3 yog Lewis puag, vim tias nws tuaj yeem pub cov electron khub ntawm nitrogen. Na2CO3 yog Bronsted- Lowry puag tsis muaj hydroxide pawg, tab sis muaj peev xwm txais hydrogens.
Bases muaj cov xab npum nplawm zoo li kev xav thiab iab saj. Lawv hnov mob yooj yim nrog cov kua qaub ua dej thiab ntsev molecules. Caustic soda, ammonia, thiab ci dej qab zib yog qee yam ntawm cov hauv paus uas peb tuaj hla ntau zaus. Cov hauv paus tuaj yeem muab faib ua ob, raws li lawv lub peev xwm los cuam tshuam thiab tsim cov hydroxide ions. Lub hauv paus muaj zog zoo li NaOH thiab KOH yog tag nrho ionized hauv kev daws teeb meem, muab ions. Cov hauv paus tsis muaj zog xws li NH3 yog ib feem ntawm kev sib cais thiab muab cov hydroxide ions tsawg dua. Kb is the base dissociation constant. Nws muab ib qho kev qhia txog lub peev xwm poob hydroxide ions ntawm lub hauv paus tsis muaj zog. Cov kua qaub uas muaj pKa tus nqi (ntau tshaj 13) yog cov acids tsis muaj zog, tab sis lawv cov conjugate bases suav tias yog cov hauv paus muaj zog. Txhawm rau xyuas seb cov khoom puas yog lub hauv paus lossis tsis yog peb tuaj yeem siv ntau qhov ntsuas xws li litmus ntawv lossis pH ntawv. Bases qhia pH tus nqi siab dua 7, thiab nws hloov liab litmus rau xiav.
Qhov txawv ntawm Nucleophilicity thiab Basicity yog dab tsi?
• Qhov txawv ntawm nucleophilicity thiab hauv paus yog ua ib tug nucleophile lossis lub hauv paus.
• Tag nrho cov nucleophiles yog lub hauv paus, tab sis txhua lub hauv paus tsis tuaj yeem yog nucleophiles.
• Lub hauv paus yog lub peev xwm los txais cov hydrogen, yog li ua cov tshuaj tiv thaiv tsis zoo, tab sis nucleophilicity yog lub peev xwm los tawm tsam electrophiles los pib ib qho tshuaj tiv thaiv.
