二乙氨基三氟化硫(DAST)是有機合成中被廣泛應用的氟化試劑,它是(二烴基氨基)三氟化硫家族中的一個成員。DAST屬於親核型氟化試劑,它能夠將醇羥基轉化成為相應的氟,將醛酮轉化成為偕二氟化物[1]。DAST將伯醇轉化成為相應氟化物的反應可以在非常溫和的條件下進行。通常在–78oC下加料來抑製最初的放熱過程,然後讓反應自動升至室溫片刻即可(式1)[2,3]。仲醇的反應雖然[
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Boc是可以說是氨基最常用的保護基了,好上又好脫。我們知道Boc最常用的方法是酸性條件脫保護,像三氟乙酸,鹽酸,甲酸,對甲苯磺酸等等。用二氯甲烷作溶劑,加三氟乙酸攪拌攪拌很容易脫除Boc;或者企業界用的比較多的氯化氫二氧六環溶液等等。
使用氯化氫溶液脫Boc的時候,含有氧雜環丁烷(TrimethyleneOxide)和氮雜環丁烷(Azetidine)結構的底物進行脫Boc的時候,就存[
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【英文名稱】NitrosoniumTetrafluoroborate
【分子式】NOBF4
【分子量】116.82
【CAS號】14635-75-7
【縮寫和別名】NitrosylTetrafluoroborate
【物理性質】無色結晶狀固體,mp250℃(升華),d2.185g/cm³,溶於乙腈溶劑中。
【製備和商品】國際大型試劑公司有銷售。
【注意事項】容易潮解,須在無水條件下使用和儲存。
四氟硼酸亞硝是一種溫和的單電子轉移氧化劑,NO/NO?在乙睛[
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TBAF釋放的氟離子可與矽原子形成穩定的Si-F鍵,廣泛應用於去矽烷基反應,這類反應通常可以在比較溫和的條件下進行,且產率很高,是切斷Si-O、Si-C等共價鍵的常用方法【氟離子對Si-O鍵和Si-C鍵的斷裂】。另外TBAF還可以用於氟取代反應製備氟化物,用於催化Hiyama交叉偶聯反應。TBAF是一種非常常見的試劑,但是其後處理非常讓人頭疼,很難純化幹淨,反相柱層析或製備液相分離[
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pulprog:PulseProgram,suchas
TDTimeDomainThisspecifiesthenumberdatapointstobetakenwiththespecifiedspectrum.AhighervalueforTDincreasesresolution,butalsoincreasesoverallacquisition
time.TDvaluesaretypicallysettoapowerof2value(i.e.65536).
NSNumberofscansThisissimplythenumberofscans.Increasingthenumberofscansincreasessignal‐to‐noiseratio,butalsoincreasesoverallexperimenttime.
...[
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Manystudentsaskthisquestion.Youshouldcollectenoughscansuntilthesignal-to-noiseratioisadequateforyourneeds.ForNMRmeasurements(wheresaturationisnotaproblem)thesignal-to-noiseratioincreasesasthesquarerootofthenumberofscans.Inordertodoublethesignal-to-noiseratioinaparticularspectrumonemustcollect4timesasmanyscansaswerecollectedintheoriginalspectrum.Takealookatthefigurebelowwherespectraareplottedonanab...[
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Allofyouroutinelyuseprotondecouplinginyour31PNMRspectra,manyofyouwithoutgivingitathought.Fewpeoplerealizethatitisasimplemattertodecouple31Pinyour1HNMRspectra.Thiswillallowyoutodeterminewhichprotonsarecoupledtophosphorus.Anexampleofthisisshownbelow.Thelowertraceisastandard1Hspectrumandtheuppertraceisa1Hspectrumwith31Pdecoupling.[
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Ithasalwayspuzzledmehowstudentssowillinglyacceptthefactthat13CisJcoupledtoaspinI=1nucleuslike2H(eg.themultipletsforthe13Cspectraofdeuteratedsolvents)howevertheydonotquestionthefactthat13CalmostnevershowsaJcouplingto14N(anotherspinI=1nucleus).Thereasonthat13CexhibitsJcouplingto2Histhattherelaxationamongthethreeenergylevelsof2Hisratherslowandeach13C"sees"the2HineachofitsthreeZeemanstates,s...[
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HereareyouroptionsoncollectingNMRdatawhenyouhaveonlyalimitedamountofsample.1.Useastandardsetupandgetmoresampleorcollectmorescans.Yeahyeah.....Iknow.....ifyoucoulddothisyouwouldn'thaveaproblem.
2.Reducethevolumeofthesolutionkeepingthesa...[
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ThereceivergainofanNMRspectrometerismuchlikethevolumecontrolonaradio.WhenitissettoohightherewillbedistortionintheNMRsignal.TheFIDwillbeclippednearthebeginningofthesignal.TheFouriertransformofthisdistortedsignalisadistortedNMRspectrum.Thefigurebelowshowswhatthisdistortionlookslike.
Manyspectrometerswillcalculatethereceivergainautomaticallyhoweveryoushouldbeawarethatthisautomaticcalculationis...[
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