Usedtirestreadcanbeupto90%,buttheaverageis6-8/32”.Tiresingoodconditionshouldhaveaminimumof6/32”tobeuseful,or4/32”ifthetireis13-14”.Theaveragelegalminimumtreaddepthis2/32”,butdrivingbecomesunsafewithsuchatread.Besides,mostdealershipsrequireatleast4/32”treadtotrade-inacarwithoutprioratirechange.
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Weathering
Weatheringisamajorfactorforthetiresonyourvehicle.Theyareendlesslyexposedtotheelements(heat,cold,snow,iceandwater).Becauserubberisanaturalmaterialandwillbreakdownovertime,youneedtobeawareofthepotentialsignsofweathering.Commonindicatorsarefinecracksinthesidewallandinbetweenthetreadblocks.Ifyoudodiscoverthesecracks(whichwillexposetheinternalmaterialsofthetiretotheelements),yourtires...[
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InpreviouspostsonthisBLOG,examplesof1H/2Hand12C/13Cisotopeeffectswerediscussed.Thefigurebelowshowsanexampleofa10B/11Bisotopeeffectobservedinthe19FNMRspectrumoftetrabutylammoniumtetrafluorobarate.Thespectrumclearlyshowstworesonancesseparatedby0.05ppmwithanintensityratioofapproximately20:80correspondingtothenaturalabundancesof10Band11B,respectively.Thelowfrequencyresonanceisdueto11BF4-.Since11Bisasp...[
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Theappearanceofthe1HNMRsignalsofproticsamplesinaproticsolventsdependscriticallyontheconcentrationofthesample.The-OH,-NH2or-COOHsignalscanhavechemicalshiftvaluesandlinewidthsoverawiderangeduetovaryingextentsofhydrogenbondingandchemicalexchange.TheconcentrationcanalsodeterminewhetherornotoneisabletoobserveJcouplingbetweenand-OHprotonandotherprotonsinthesample.Anexampleofthisisillustratedbelow.Thefig...[
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在試管中加入少量（麥粒大小）待結晶物，加入0.5mL根據上述規律所選擇溶劑，加熱沸騰幾分鍾，看溶質是否溶解。若溶解，用自來水衝試管外測，看是否有晶體析出。[
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WhyAre1HNMRIntegrationsNotPerfect?AnInquiry-BasedExerciseforExploringtheRelationshipbetweenSpinDynamicsandNMRIntegrationintheOrganicLaboratorHaimWeizmanDepartmentofChemistryandBiochemistry,UniversityofCalifornia,SanDiego,LaJolla,CA92093-0303;hweizman@ucsd.edu
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1,1'-Carbonyldiimidazole(CDI)isanorganiccompoundwiththemolecularformula(C3H3N2)2CO.Itisawhitecrystallinesolid.Itisoftenusedforthecouplingofaminoacidsforpeptidesynthesisandasareagentinorganicsynthesis.CDIismainlyemployedtoconvertaminesintoamides,carbamates,ureas.Itcanalsobeusedtoconvertalcoholsintoesters.AcidderivativesTheformationofamideispromotedbyCDI.AlthoughthereactivityofCDIislessthanacidc...[
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TheEschweiler–Clarkereaction(alsocalledtheEschweiler–Clarkemethylation)isachemicalreactionwherebyaprimary(orsecondary)amineismethylatedusingexcessformicacidandformaldehyde.Reductiveaminationreactionssuchasthisonewillnotproducequaternaryammoniumsalts,butinsteadwillstopatthetertiaryaminestage.ItisnamedfortheGermanchemistWilhelmEschweiler(1860–1936)andtheBritishchemistHansThacherCla...[
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酯可以說是合成化學中最常見的官能團了，除了廣泛存在於活性分子中，也是羧酸最常用的保護基了。常見的酯有叔丁酯，甲酯，乙酯，苄酯，烯丙醇酯，還有三氯乙醇酯等等，水解方法各不相同，有加堿的，有氫化脫苄基的，有鋅粉還原脫保護的。對於非手性的酯，隻要拿到產物就可以，沒有手性問題需要考慮。然而對於手性的酯，如果消旋了，就非常的麻煩。在眾多酯當[
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NMRspectroscopyisuniqueamongspectroscopicmethodsinthatthattherelaxationprocessesarerelativelyslow(ontheorderofsecondsortenthsofseconds),comparedtoms,us,andpico-secondsforIRandUV.Inotherwords,oncethespectrometerhasperturbedtheequilibriumpopulationofnucleibypulsingattheresonancefrequency,ittakesfrom0.1to10sofsecondsforthemtoreturntotheiroriginalpopulations.Typically,onemeasurestheT1(spin-latticerela...[
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