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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在试管中加入少量（麦粒大小）待结晶物，加入0.5mL根据上述规律所选择溶剂，加热沸腾几分钟，看溶质是否溶解。若溶解，用自来水冲试管外测，看是否有晶体析出。[
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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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酯可以说是合成化学中最常见的官能团了，除了广泛存在于活性分子中，也是羧酸最常用的保护基了。常见的酯有叔丁酯，甲酯，乙酯，苄酯，烯丙醇酯，还有三氯乙醇酯等等，水解方法各不相同，有加碱的，有氢化脱苄基的，有锌粉还原脱保护的。对于非手性的酯，只要拿到产物就可以，没有手性问题需要考虑。然而对于手性的酯，如果消旋了，就非常的麻烦。在众多酯当[
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NMRspectroscopyisuniqueamongspectroscopicmethodsinthatthattherelaxationprocessesarerelativelyslow(ontheorderofsecondsortenthsofseconds),comparedtoms,us,andpico-secondsforIRandUV.Inotherwords,oncethespectrometerhasperturbedtheequilibriumpopulationofnucleibypulsingattheresonancefrequency,ittakesfrom0.1to10sofsecondsforthemtoreturntotheiroriginalpopulations.Typically,onemeasurestheT1(spin-latticerela...[
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