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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ManyNMRusers(oftheorganicvariety)cometobelievethatall13Cresonancesaresingletsasthemostcommonwaytocollectthedataiswithprotondecoupling,whichindeedreducesmost13Cresonancestosinglets.Itisasurprisetosometofindmultiplicityinthe13Cresonanceswhenanucleussuchas31Por19Fispresentinthemolecule.Belowisthearomaticregionoftheprotondecoupled13CNMRspectrumofalpha,alpha,alpha-trifluoro-p-tolualdehyde(thealdehydepe...[
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Ihaveseensomestudentscollect31PNMRdatawithoutprotondecoupling.Theirreasonwasthattherewerenodirectlyboundprotonstothephosphorus.Whattheyhavenottakenintoaccountaretheremoteprotonswhichhavesmallcouplingstothephosphorus.Thereareusuallymanyoftheseremoteprotonsandthecumulativeeffectofthecouplingsistobroadenoutthe31Presonance.Thisbroadeningcausesaseverelossinthesignal-to-noiseratio.Theuppertraceofthefigu...[
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TriturationTechniquesTriturationcanbedefinedasthepurificationofanimpurecompoundbytakingadvantageofthesolubilitydifferencesofthecompoundvsitsimpuritiesinasolvent(orsolventmixture).Belowarethreecommontriturationtechniques.A)Suspend&Filter Findanappropriatesolvent(orsolventmixture).Thesolventshouldbeoneinwhichyourpdtissparinglysolubleandyourimpuritiesarehighlysoluble. Suspendyourcrudepdtinthesolv...[
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TheTASFreagentortris(dimethylamino)sulfoniumdifluorotrimethylsilicateisareagentinorganicchemistrywithstructuralformula[((CH3)2N)3S]+[F2Si(CH3)3]−.Itisananhydroussourceoffluorideandisusedtocleavesilyletherprotectivegroups.Manyotherfluoridereagentsareknown,butfewaretrulyanhydrous,becauseoftheextraordinarybasicityof"naked"F−.InTASF,thefluorideismaskedasanadductwiththeweakLewisac...[
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催化反应中的溶剂效应液相催化加氢是有机化学中广泛应用的一类反应。研究表明，所用溶剂的性质对反应的速率和选择性有显著的影响。有文献提出了几个可能的原因来解释溶剂对反应的影响。包括：(i)氢气在反应介质中的溶解度；（ii）溶剂在活性催化剂部位的竞争性吸附；（iii）催化剂在某些溶剂中的聚集；（iv）反应物与溶剂分子之间的相互作用。另外，也有文献认为[
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，碱性条件下，杂环胺取代OMs，进行N-烷基化反应。在这个反应中，发现SM2的当量需求较大。并且观测到一个主要的杂质，后来鉴定为噁唑烷酮IM，结构如下图所示。很明显，该杂质源于SM2自身的分解，即Boc对OMs的亲核取代。这也解释了SM2需要大大过量的原因。除了Boc胺基醇底物，只要N-Boc附近有合适的离去基，就可能发生上述反应。比如苄溴类化合物1，其稳定性不是很好，在4[
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