Name: moisture-free setup for organic reactions
Uploaded: 2023-04-30T06:47:26.000Z
Duration: 10 min 17 s
Channel: JoVE

K12 Standards

new-york-state-science-learning-standards

New York State Science Learning Standards

High School

Physical Science

HS. Structure and Properties of Matter

HS-PS1-10.

preparing-anhydrous-reagents-and-equipment

Preparing Anhydrous Reagents and Equipment

玻璃器皿的干燥
1. 烘箱干燥
<ol>
	<li>移除所有非玻璃材质的部件，例如滴液漏斗的活塞。</li>
	<li>将装置中所有玻璃器皿置于设定为约 125 °C 的烘箱中干燥至少 24 小时，使用前保持在此条件下。</li>
	<li>戴上隔热手套，从烘箱中取出玻璃器皿。组装装置时，务必小心处理高温玻璃器皿。</li>
	<li>为获得最佳效果，在组装装置时应通入惰性气体（如 N2&#160;）进行吹扫。</li>
</ol>
2. 火焰干燥
<ol>
	<li>安装完整的装置，但移除所有非玻璃材质的组件（如滴液漏斗的活塞或橡胶套管等）。此时不要在装置上连接任何管路。</li>
	<li>戴上耐热手套。</li>
	<li>设置本生灯，仔细对装置进行火焰干燥。从底部开始，向上移动火焰，&#34;伴随&#34;水分一起排出。过程中会产生蒸汽并使玻璃器皿起雾。持续火焰干燥，直至起雾现象消失。</li>
	<li>等待装置冷却至约 60 °C。此过程需要几分钟，此时玻璃表面仍微热，但短时间接触不会造成烫伤。</li>
	<li>小心安装其余非玻璃部件，例如管路和活塞。操作装置时请勿摘下耐热手套，以防烫伤。</li>
	<li>待所有部件正确组装后，用惰性气体（如 N2）吹扫装置，以加速玻璃器皿冷却至可加入试剂的温度。</li>
</ol>
注意：在火焰干燥过程中，除非实验步骤特别要求，切勿将任何溶剂、磁力搅拌子或任何试剂放入烧瓶中。（然而，在进行格氏反应时，火焰干燥过程中可将镁屑留在烧瓶内。）
3. 用丙酮干燥
<ol>
	<li>用丙酮冲洗玻璃器皿。</li>
	<li>将丙酮冲洗液收集至指定的溶剂废液容器中。</li>
	<li>用 N2 气体或干燥压缩空气吹洗玻璃器皿，以加速干燥。</li>
</ol>
溶剂的干燥
1. 使用活性金属钠进行干燥
<ol>
	<li>在石油醚下小心切割钠金属，以尽量减少金属与空气反应引发燃烧的风险。金属表面会迅速氧化，产生白色残留物。将金属切成薄片，尽可能暴露更多的金属表面。</li>
	<li>在氮气（N2）氛围下，将钠屑加入含有溶剂的蒸馏烧瓶中。</li>
	<li>随后加入二苯甲酮，这是一种用于监测反应的指示剂。当体系中存在水时，溶液呈无色或黄色；而当溶剂完全干燥时，溶液变为蓝色或紫色。</li>
	<li>使用加热套回流溶液，直至观察到溶液颜色变为蓝色或紫色。</li>
	<li>蒸馏溶剂，将其收集于干燥的烧瓶中，并在冷却后立即用于后续反应。 
	废液处理：干燥过程结束后，必须安全处理蒸馏烧瓶中残留的钠。</li>
	<li>为此，小心地向钠中加入乙醇，直至不再有氢气产生。</li>
	<li>仔细但充分搅拌溶液，并确保没有残留的钠块，以免内部包裹有未反应的金属钠。</li>
	<li>小心地向混合物中加入甲醇，并将混合物置于通风橱后部静置数小时，以确保钠完全反应。</li>
	<li>最后，将混合物极其小心地加入大量过量的水中，并将最终溶液倒入适当的废液收集容器中处理。</li>
</ol>
2. 分子筛干燥
<ol>
	<li>打开装有分子筛的瓶子，将其倒入耐热玻璃烧杯中。为便于后续使用，可干燥多于当前实验所需的量。</li>
	<li>活化时，将装有分子筛的烧杯放入高温烘箱中，在 300–350 °C 下加热 3–3.5 小时。或者，如有条件，可在真空烘箱中于 200 °C 下加热相同时间。</li>
	<li>使用耐高温手套将装有分子筛的烧杯取出，并置于普通干燥烘箱中，温度保持在 120 °C 以上。或者，也可将烧杯置于干燥器内保存。分子筛可在使用前保存数周。</li>
	<li>从干燥烘箱或干燥器中取出装有分子筛的烧杯。自此步骤起应迅速操作，以尽量减少分子筛与空气中水分的接触。</li>
	<li>若从烘箱中取出分子筛，需使其冷却至接近室温。冷却期间用干燥的毛巾覆盖烧杯，以减少其暴露于空气。</li>
	<li>为检测分子筛是否仍具活性，戴上一次性手套，取少量分子筛置于手心，加入约两倍体积的水。若分子筛明显发热，则表明其已活化。</li>
	<li>在天平上称取所需量的活化分子筛。例如，若需在 500 mL 溶剂中达到 10% m/v 的分子筛浓度，则需 50 g 分子筛。</li>
	<li>将处于室温的分子筛加入新开启的溶剂瓶中。务必确保分子筛已冷却，尤其是当溶剂具有挥发性时。切勿在分子筛从烘箱取出后立即直接加入溶剂中。</li>
	<li>对于挥发性溶剂（如 DCM），可先将瓶盖置于瓶口上，数分钟后待内部压力平衡再完全旋紧，以避免压力积聚。</li>
	<li>用 Parafilm 密封瓶盖周围区域，防止湿气进入。</li>
	<li>将溶剂在分子筛上静置适当时间，例如 24 小时。</li>
</ol>
试剂的干燥
1. 萃取后有机相的干燥
<ol>
	<li>在分液漏斗中两相分离后，将有机相转移至干燥的玻璃容器中，例如烧杯或锥形瓶（小规模操作可使用试管）。</li>
	<li>加入干燥剂 表2 （通常为 NaSO）4或 MgSO₄4) 用刮勺将干燥剂加入有机相。最初干燥剂会结块。</li>
	<li>继续加入干燥剂，直至新加入的干燥剂不再结块，且能自由滚动。此外，溶液应呈澄清状态，而非浑浊。</li>
	<li>如有，用塞子盖住玻璃容器，否则用一些铝箔覆盖。</li>
	<li>让溶液在干燥剂中静置约1小时。静置时间较长亦可，例如过夜。</li>
	<li>组装带有布氏漏斗和抽滤瓶的真空过滤装置。</li>
	<li>在布氏漏斗中放入一张滤纸，然后打开真空泵。</li>
	<li>缓慢将有机相倾倒入布氏漏斗中。最初阶段尽量避免转移干燥剂，以免堵塞滤纸。</li>
	<li>当大部分液体已转移至漏斗并流入下方的烧瓶后，将剩余的有机相连同干燥剂一并加入，静置数分钟。</li>
	<li>关闭真空泵，将有机相转移至干燥的圆底烧瓶中。</li>
	<li>将圆底烧瓶连接至旋转蒸发仪，并在减压条件下除去所有溶剂。</li>
	<li>若产物为液体，应将其保存在干燥剂上，并在使用前新鲜蒸馏。</li>
</ol>
2. 固体试剂的干燥
<ol>
	<li>将固体试剂放入敞口玻璃容器中，称量其总重量。</li>
	<li>将装有试剂的容器置于干燥烘箱中，烘箱温度应低于该固体的熔点。若条件允许，使用真空烘箱。必要时佩戴隔热手套。</li>
	<li>让试剂在烘箱中干燥数小时。</li>
	<li>从烘箱中取出装有试剂的容器。</li>
	<li>让样品冷却至室温，最好在干燥器内进行冷却。</li>
	<li>称量重量，确保其低于干燥前的重量。如有必要，重复步骤 2.2 – 2.5。</li>
	<li>待试剂冷却至室温后，即可使用。</li>
	<li>若试剂无需立即使用，可用惰性气体（如 N2）吹洗容器，盖紧瓶盖，并在瓶口缠绕封口膜（Parafilm）。</li>
	<li>将容器放入干燥器中，保存至需要使用时。</li>
</ol>
3. 热敏性固体试剂的干燥
<ol>
	<li>通过在干燥器的下部放置新鲜的无水干燥剂来准备干燥器（通常使用 P2O5）。</li>
	<li>将固体试剂放入一个开口的玻璃容器中，并称量其质量。</li>
	<li>将装有试剂的容器放入干燥器内。</li>
	<li>盖上干燥器盖子，从侧面水平滑动盖紧，以确保密封良好。</li>
	<li>通过活塞连接对干燥器抽真空。</li>
	<li>数分钟后关闭活塞，并关闭真空泵。</li>
	<li>让试剂在干燥器中至少干燥数小时。</li>
	<li>打开干燥器上的活塞，使空气流入。</li>
	<li>小心地从侧面水平滑开干燥器盖子，切勿尝试垂直向上提起盖子。</li>
	<li>从干燥器中取出试剂并称重，其质量应比干燥前有所降低。</li>
	<li>如有必要，重复步骤 3.3 至 3.10，直至质量保持恒定且试剂完全干燥。</li>
	<li>如果试剂不需要立即使用，可用惰性气体&#160;（如 N2&#160;）吹洗容器，盖紧盖子，并在盖子周围包裹 Parafilm。</li>
	<li>将容器放入干燥器中，保存至需要使用该试剂时。</li>
</ol>

无水试剂与仪器的准备

来源：Dana Lashley 博士实验室 - 威廉与玛丽学院 
演示者：Timothy Beck 和 Lucas Arney
有机化学中的许多反应对水分敏感，必须在严格排除水分的条件下进行。在这些情况下，试剂极易与空气中的水分发生反应，若暴露于空气中，目标反应将无法发生或产率很低，因为反应物的化学性质已发生改变。
为了防止与 H2O 发生不期望的反应，这些反应必须在惰性气氛下进行。惰性气氛可通过在氮气下进行反应来实现，而在更敏感的情况下，则可在氩气等稀有气体气氛下进行。
此类反应中的每个组分都必须完全无水，即不含水分。这包括使用的所有试剂和溶剂，以及所有会接触试剂的玻璃器皿和设备。对水分极为敏感的反应必须在手套箱内进行，手套箱提供一个完全密闭的无水环境，操作者可通过从箱体侧面伸出的一对手套在其中操作。

必须在无水条件下进行的反应的经典例子是格氏反应。（方程式 1）
<img alt="格氏反应机理图：乙醚、淬灭、酮转化为醇。" src="/files/ftp_upload/10227/10227eq1.jpg" data-altupdatedat="1761830439000" data-alt="方程">
在反应的第一步中，格氏试剂 RMgX 作为亲核试剂进攻亲电试剂（本例中为酮）。此步骤中，必须确保不存在任何微量的水。格氏试剂虽然是一种强亲核试剂，但其碱性更强。在水的存在下，它会优先作为碱夺取水的质子，导致亲核性的格氏试剂失活，并生成烷烃这一不希望得到的副产物。（方程式 2）
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来源：Dana Lashley 博士实验室 - 威廉与玛丽学院  
演示者：Timothy Beck 和 Lucas Arney  
有机化学中的许多反应是……

对水分敏感的化学反应必须在无水环境中进行。试剂和反应物有时会与空气中的水分发生反应或吸收水分。如果发生这种情况，试剂的化学或物理性质可能发生改变，导致预期的反应无法进行或产率低下。为防止与水发生不期望的反应，敏感反应需在惰性气氛（如氮气或氩气）下进行，并使用无水试剂和仪器。对水极其敏感的反应必须在手套箱内进行，以维持无水环境。本视频将演示如何正确干燥玻璃器皿、溶剂和试剂，以开展无水反应。玻璃的化学成分会导致其表面形成一层水膜，在进行无水反应前必须去除该层水膜。通常在使用前，通过加热或丙酮处理来清除洁净玻璃器皿表面的这一水层。许多溶剂也会从环境中吸收水分，因此在使用前必须进行干燥。在搭建反应体系之前，通常使用溶剂蒸馏装置或干燥剂去除水分。溶剂纯化装置使用钠等碱金属与水反应，使残留水分含量降至约百万分之十。干燥剂是吸湿性很强的固体，意味着它们容易吸收水分。某些干燥剂（如硫酸钠）可用于去除少量有机溶剂中的水分，在进一步使用前必须通过过滤除去。分子筛是最常用的干燥剂，用于干燥较大量溶剂。它由微孔材料构成，主要成分为硅铝酸钠和硅铝酸钙。分子筛通过将水分子截留在珠状颗粒内部，从而有效地从溶剂中去除水分。使用后，可通过烘箱加热再生。最后，干燥固体试剂有多种方法。一种方法是在温度设定为其熔点以下15–20 °C的烘箱中储存。热量可驱除试剂中的水分，留下干燥的化合物。如果该固体无法加热或熔点过低，则可在真空干燥器中进行干燥。干燥后，无水试剂可储存于干燥器内的惰性气氛中的瓶中。现在您已经了解了无水反应中干燥仪器和试剂背后的原理，接下来让我们仔细观察一下在实验室中是如何实际操作的。将玻璃器皿放入烘箱干燥时，首先收集反应装置所需的所有组件。移除所有非玻璃材质的部件，例如施伦克烧瓶的活塞。将玻璃器皿放入设定为 125 °C 的干燥烘箱中，在使用前至少烘烤 24 小时。24小时后，戴上隔热手套，将玻璃器皿从烘箱中取出。在玻璃器皿仍然温热时组装装置。当玻璃仪器完全组装并冷却后，用惰性气体（如氮气）冲洗装置。最后，将干燥前移除的部件重新安装。此时，玻璃仪器已准备好用于无水反应。相比使用烘箱干燥玻璃器皿，更快的方法是使用本生灯。某些玻璃器皿不应进行火焰干燥，因此在开始前务必确认装置适合火焰干燥。首先，安装完整的装置，并移除所有非玻璃材质的部件。戴上耐热手套，然后点燃本生灯。通过加热装置底部开始对玻璃器皿进行火焰干燥。将火焰向上移动，以驱除装置中的水分。持续此操作，直至雾化和蒸汽现象停止。等待装置冷却至约 60 °C，然后使用耐热手套，重新安装之前为火焰干燥而拆下的其余装置部件。使用分子筛干燥溶剂时，首先将其加入耐热玻璃容器中。筛子必须先干燥才能正常操作，因此将容器放入300至350 °C的烘箱中，烘烤3 ± 0.5小时。当分子筛珠干燥后，使用耐高温手套取出容器，并将其置于温度高于120??C的干燥烘箱中储存。干燥后的分子筛可在使用前储存数周。如需使用，从干燥箱或干燥器中取出珠粒。操作需迅速，并从此时起盖好容器，以尽量减少珠粒与空气中的水分接触。若从烘箱中取出珠子，请让其冷却至大约室温。在天平上称取所需量的活性珠。例如，若要在500 mL溶剂瓶中达到10%的质量与体积比的珠量，则需要50 g珠。将珠子加入溶剂中。对于挥发性溶剂（如二氯甲烷），先将瓶盖置于瓶口上方，但不要立即完全拧紧，等待几分钟后再完全拧紧瓶盖，以避免压力积聚。用帕拉膜（Parafilm）包裹瓶盖周围区域以密封，防止湿气进入。将溶剂与分子筛一起储存至少24小时。此后，无水溶剂即可用于反应。或者，可使用金属钠和二苯甲酮的溶剂蒸馏装置来干燥溶剂。固体试剂通常溶解在有机溶剂中。在去除液体并回收固体试剂之前，必须从溶液中除去多余的水分。取一个干燥的容器并加入溶液。然后用刮勺将干燥剂加入容器中。干燥剂最初会结块，需继续添加，直至新加入的干燥剂不再结块并能自由流动为止。用塞子或铝箔封住容器，静置溶液至少1小时。为去除多余的干燥剂，使用布氏漏斗和抽滤瓶组装真空过滤装置。在布氏漏斗中放入滤纸，然后打开真空泵。缓慢将有机相倾倒入布氏漏斗中。避免转移干燥剂，以免堵塞滤膜。当大部分液体已转移至漏斗并流入下方烧瓶后，将剩余部分连同干燥剂一同加入，并静置数分钟。关闭真空泵，将滤液转移至干燥的圆底烧瓶中。将圆底烧瓶连接至旋转蒸发仪，在减压条件下除去所有溶剂。残留的固体或液体此时应已干燥。要干燥一种已呈固态的试剂，可将该化合物置于敞口容器中并称重。然后将其放入干燥箱内，干燥箱的设定温度应低于该固体的熔点。让试剂在干燥箱内干燥数小时。将容器从烘箱中取出，放入干燥器中，然后让样品冷却至室温。重新称重，确保质量低于烘干前的质量。重复干燥步骤，直至重量不再变化。当重量恒定时，说明试剂已充分干燥。如果试剂不需要立即使用，应用惰性气体（如氮气）吹扫容器，并在瓶盖上包裹封口膜。将容器放入干燥器中，保存至需要使用该试剂时。无水反应被用于多种重要的有机化学合成中。一个必须在无水条件下进行的典型反应是格氏反应。在该反应的第一步中，必须确保即使是最微量的水分也不能存在。如果存在水，格氏试剂将优先作为碱起反应，导致其失去亲核活性，并生成不希望的副产物。许多有机合成必须在极度干燥的条件下进行，例如本例中的有机磁体合成。该反应的前体材料为金属钠，具有自燃性，这意味着它对水分极为敏感，接触空气中的水分时可能燃烧甚至发生爆炸。锂离子电池对湿气也极为敏感，必须在手套箱或干燥间内组装。负极由一种锂化合物构成，而电解质则含有卤化锂盐。由于锂对湿气敏感，任何微量水分进入电池内部都会降低其容量。您刚刚观看了 JoVE 关于无水试剂和仪器准备的简介。现在，您应该了解如何准备用于化学反应的无水玻璃器皿、溶剂和试剂。感谢观看！

Education

教育

JoVE Science Education

Chemistry

化学

Organic Chemistry

有机化学

制备无水试剂和设备

moisture-free setup for organic reactions

Many organic reactions must be set up without water. Moisture in the air can react with sensitive reagents before the reaction even starts. When that happens, the desired reaction may fail or give poor yields because the reactants have changed chemically.

To prevent this, the reaction is run under an inert atmosphere. An inert atmosphere is a gas environment that does not react easily with the chemicals in the flask. Nitrogen gas is often used, and argon may be used for reactions that are even more sensitive.

Every part of the setup must be anhydrous, meaning free of water. That includes the reagents, the solvents, the glassware, and any equipment that will touch the chemicals. For extremely water-sensitive work, the reaction is done inside a glovebox. A glovebox is a sealed chamber that keeps out moisture and lets the chemist work through built-in gloves.

Moisture-Free Setup for Organic Reactions

moisture-free-setup-for-organic-reactions

introduction to catalysis

Catalysis in Industry and Sustainability

Catalysis is a major part of modern technology. It helps chemical reactions happen by lowering activation energy, which is the energy needed to start a reaction. Catalysts can also affect selectivity, or which products form during a reaction. Catalysis has a large impact on industry and daily life. It is linked to about 35% of global GDP. It also supports the food supply for about 33% of the world’s population through fertilizers made by the Haber process. Because catalysts improve how...

assembly of a reflux system for heated chemical reactions

assembly-of-a-reflux-system-for-heated-chemical-reactions

Reflux Setup for Heating Reactants Safely

A reflux setup lets chemists heat reactants without losing material to evaporation. Many chemical experiments need elevated temperatures before a reaction starts. When the reactants or solvent have low boiling points, heating can cause them to escape as vapor. A reflux system prevents that loss by condensing the vapor that forms during heating. The condensed liquid then flows back into the reaction vessel. This keeps the reactants and solvent in the flask while the reaction is heated.

conducting reactions below room temperature

conducting-reactions-below-room-temperature

Cooling Baths for Low-Temperature Reactions

Low-temperature reactions are often run with cooling baths to keep the reaction flask below room temperature. Chemists use this setup when they want a reaction to stay within a specific temperature range. The reagents in the flask do not touch the cooling bath itself. Reaction rate depends on molecular collisions. At higher temperatures, atoms and molecules move faster, collide more often, and react more effectively. A common rule of thumb based on the Arrhenius equation says that raising the...

schlenk lines transfer of solvents

Air-Free Solvent Transfer by Vacuum

Schlenk lines and high vacuum lines are used to move solvents without exposing them to moisture or oxygen. They do this by keeping reactions under a slight overpressure of inert gas, usually nitrogen or argon, or by using vacuum. Vacuum transfer is a separate method for isolating solvents and other volatile reagents from drying agents or other nonvolatile materials. It lets users dispense clean solvent into a reaction vessel or storage vessel while the air-free environment is maintained. The...

degassing liquids with freeze-pump-thaw cycling

degassing-liquids-with-freeze-pump-thaw-cycling

Freeze-Pump-Thaw for Removing Dissolved Gases

Freeze-pump-thaw cycling is a method for removing dissolved gases from a liquid. Degassing means taking dissolved gases out of a liquid. These gases can include oxygen or carbon dioxide. Dissolved gases can cause problems in the lab. They can interfere with chemical reactions that use sensitive reagents. They can also affect spectroscopic measurements and cause unwanted bubble formation. Several methods can be used to degas liquids. These include heating, ultrasonic agitation, chemical...

preparing anhydrous reagents and equipment

Many organic reactions must be set up without water. Moisture in the air can react with sensitive reagents before the reaction even starts. When that happens, the desired reaction may fail or give poor yields because the reactants have changed chemically. To prevent this, the reaction is run under an inert atmosphere. An inert atmosphere is a gas environment that does not react easily with the chemicals in the flask. Nitrogen gas is often used, and argon may be used for reactions that are even...

purifying compounds by recrystallization

Recrystallization for Solid Compound Purity

Recrystallization is a technique for purifying solid compounds. It uses the fact that solids are often more soluble in hot liquids than in cold liquids. An impure solid is dissolved in a hot liquid until the solution becomes saturated, meaning it holds as much dissolved material as it can at that temperature. The solution is then allowed to cool. As the temperature drops, the compound should form relatively pure crystals. Most impurities should stay in the solution and not become part of the...

separation of mixtures via precipitation

Solubility-Based Mixture Separation

Solubility-based separation removes a compound from a mixture by making it insoluble in water. Most samples of interest contain many different components, so sample preparation is an important step before analysis. It helps remove interferences that could affect the results. This separation method is useful in both academic and industrial settings. The process relies on the solubility properties of compounds in aqueous solutions. A compound’s solubility can depend on ionic strength, pH, and...

solid-liquid extraction

Solvent Separation in Solid Samples

Solid samples can be prepared for chemical analysis by moving the target analyte into a liquid. This solid-liquid extraction step is used in many chemical analyses before spectroscopic or chromatographic identification and quantification. It helps separate the analyte from the rest of the sample matrix, which is the material surrounding it. A simple approach is to mix the solid with a solvent that can dissolve the analyte. Agitation helps the analyte leave the solid and partition into the...

rotary evaporation to remove solvent

Rotovap Use in Organic Chemistry

Rotary evaporation is a common lab method for drying and purifying samples in organic chemistry. It helps remove a solvent from a compound of interest when the compound has a higher boiling point. A rotary evaporator is often called a rotovap. The rotovap was invented in 1950 by the chemist Lyman C. Craig. It is widely used because it works quickly and can handle large volumes of solvent. For this reason, many laboratories prefer rotary evaporation when they need to remove low boiling point...

fractional distillation

Separating Liquids by Boiling Point

Fractional distillation separates liquid mixtures by using differences in boiling point. Chemists use this lab technique to purify organic liquids. When a mixture is carefully distilled, compounds with different boiling points split into individual parts. There are two main types of distillation: simple distillation and fractional distillation. Simple distillation is used when a liquid is relatively pure, when it contains no more than 10% liquid contaminants, or when it has a non-volatile...

growing crystals for x-ray diffraction analysis

growing-crystals-for-x-ray-diffraction-analysis

X-ray Crystal Growth for Structure Analysis

X-ray crystal growth is a key step in X-ray crystallography, the method used to determine the spatial arrangement of atoms in a crystalline solid. That structure reveals the three-dimensional shape of a molecule or complex. Since structure and function are closely linked, this information can help explain a compound's behavior and reactivity. X-ray crystallography is one of the most useful ways to solve a compound's three-dimensional structure. In some cases, it may be the only practical...

performing 1d thin layer chromatography

Thin Layer Chromatography for Mixture Separation

Thin layer chromatography separates mixtures of non-volatile compounds. It uses a TLC plate with a thin layer of adsorbent material as the stationary phase. The adsorbent layer is fixed to a solid support such as plastic, aluminum, or glass. The sample and a reference compound are first dissolved in a suitable solvent. They are then applied as small spots near the bottom edge of the TLC plate. This placement helps the compounds move with the developing solvent in a controlled way. To run the...

column chromatography

Purifying Compounds with a Chromatography Column

Column chromatography is a useful method for purifying compounds. It uses a stationary phase packed into a column and a mobile phase that flows through it. The separation works because different molecules have different polarities, so they move through the column at different rates. The most common stationary phases are silica gel, or SiO2, and alumina, or Al2O3. The mobile phase is usually an organic solvent. The solvent choice depends on the polarity of the molecules being purified. More...

nuclear magnetic resonance (nmr) spectroscopy

nuclear-magnetic-resonance-nmr-spectroscopy

Using NMR to Track Organic Reactions

Nuclear magnetic resonance (NMR) spectroscopy helps organic chemists study molecules and check reaction results. It can show molecular structure, sample content, and sample purity. Because NMR is non-destructive, it is useful when the sample needs to be recovered after analysis. One of the most common methods is proton, or 1H, NMR. Protons in a molecule respond differently depending on their chemical environment. That difference makes it possible to infer the structure of the molecule from the...

organic chemistry

该系列的特点是在有机化学实验室中经常使用的技术, 侧重于在化学反应和 post-reaction 细化过程中调节温度和气氛。

Learn how moisture-sensitive organic reactions use inert gas, dry reagents, anhydrous glassware, and gloveboxes to keep water out of the setup.

Moisture-Free Setup for Organic Reactions | JoVE K12

HS. Chemical Reactions

HS-PS1-2.

HS-PS1-5.

HS-PS1-7.

Dana Lashley

Overview

Principles of Preparing Anhydrous Reagents and Equipment

Drying Glassware

Drying Solvents

Drying Reagents

Applications

Summary

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Electron Orbital Model

Orbitals are the areas outside of the atomic nucleus where electrons are most likely to reside. They are characterized by different energy levels, shapes, ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

Coordination Chemistry Complexes

Source: Laboratory of Dr. Neal Abrams &#8212; SUNY College of Environmental Science and Forestry
Transition metals are found everywhere from vitamin ...

Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.

HS-PS1-1.

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

The Born-Haber Cycle

Lattice Energy&#xA0;

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a ...

trends-in-lattice-energy-ion-size-and-charge

Trends in Lattice Energy: Ion Size and Charge

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Electronegativity

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

Electronegativity values of ...

bond-polarity-dipole-moment-and-percent-ionic-character

Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

The absolute value of the difference in electronegativity (&Delta;EN) of two bonded atoms provides a rough measure of the polarity to be ...

lewis-structures-of-molecular-compounds-and-polyatomic-ions

Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

Resonance

The Lewis structure of a nitrite anion (NO2&minus;) may actually be drawn in two different ways, distinguished by the locations of the N-O and N=O ...

Formal Charges

In some cases, there are seemingly more than one valid Lewis structures for molecules and polyatomic ions. The concept of formal charges can be used to ...

Exceptions to the Octet Rule

Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:


	...

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Dr&#xFC;de called the ...

VSEPR Theory and the Basic Shapes

Overview of VSEPR Theory

Valence shell electron-pair repulsion theory (VSEPR theory) enables us to predict the molecular structure, including approximate ...

vsepr-theory-and-the-effect-of-lone-pairs

VSEPR Theory and the Effect of Lone Pairs

Effect of Lone Pairs of Electrons&nbsp;on Molecule Geometry

It is important to note that electron-pair geometry around a central atom is not the same ...

Predicting Molecular Geometry

VSEPR Theory for Determination of Electron Pair Geometries

The following procedure uses VSEPR theory to determine the electron pair geometries and the ...

Molecular Shape and Polarity

Dipole Moment of a Molecule

Polar covalent bonds connect two atoms with differing electronegativities, leaving one atom with a partial positive charge ...

Valence Bond Theory

Overview of Valence Bond Theory

Valence bond theory describes a covalent bond as the overlap of half-filled atomic orbitals (each containing a single ...

Hybridization of Atomic Orbitals I

The mathematical expression known as the wave function, &#x3C8;, contains information about each orbital and the wavelike properties of electrons in an ...

Hybridization of Atomic Orbitals II

sp3d and sp3d&nbsp;2 Hybridization

To describe the five bonding orbitals in a trigonal bipyramidal arrangement, we must use five of the valence shell ...

Molecular Orbital Theory I

Overview of Molecular Orbital Theory

Molecular orbital theory describes the distribution of electrons in molecules in the same way as the distribution of ...

Molecular Orbital Theory II

Molecular Orbital Energy Diagrams

The relative energy levels of atomic and molecular orbitals are typically shown in a molecular orbital diagram. For a ...

Molecular Orbital (MO) Theory

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
This protocol serves as a guide in the synthesis of two metal complexes ...

Intermolecular vs Intramolecular Forces

Intermolecular forces (IMF) are electrostatic attractions arising from charge-charge interactions between molecules. The strength of the intermolecular ...

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions ...

Molecular and Ionic 
Solids

Crystalline solids are divided into four types: molecular, ionic, metallic, and covalent network based on the type of constituent units and their ...

comparing-intermolecular-forces-melting-point-boiling-point

Comparing Intermolecular Forces: Melting Point, Boiling Point, and Miscibility

Intermolecular forces are attractive forces that exist between molecules. They dictate several bulk properties, such as melting points, boiling points, ...

Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.

HS-PS1-3.

Radioactivity and Nuclear Equations

Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for ...

Types of Radioactivity

The most common types of radioactivity are &#945; decay, &#946; decay, &#947; decay, neutron emission, and electron capture.
Alpha (&#945;) decay is the ...

Nuclear Stability

Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10&#8722;15 meters, a nucleus is ...

Nuclear Binding Energy

The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect ...

Radioactive Decay and Radiometric Dating

Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. ...

Nuclear Fission

Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger ...

Nuclear Power

Controlled nuclear fission reactions are used to generate electricity. Any nuclear reactor that produces power via the fission of uranium or plutonium by ...

Nuclear Fusion

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process ...

Nuclear Transmutation

Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with ...

Biological Effects of Radiation

All radioactive nuclides emit high-energy particles or electromagnetic waves. When this radiation encounters living cells, it can cause heating, break ...

determining-rate-laws-and-the-order-of-reaction

Determining Rate Laws and the Order of Reaction

Source: Laboratory of Dr. Neal Abrams &#8212; SUNY College of Environmental Science and Forestry
All chemical reactions have a specific rate defining the ...

Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay.

HS-PS1-8.

Properties of Transition Metals

Transition metals are defined as those elements that have partially filled d orbitals. As shown in Figure 1, the d-block elements in groups 3&#8211;12 are ...

Coordination Compounds and Nomenclature

In most main group element compounds, the valence electrons of the isolated atoms combine to form chemical bonds that satisfy the octet rule. For ...

Communicate scientific and technical information about why the particulate-level structure is important in the functioning of designed materials.

HS-PS2-6.

Moisture-Free Setup for Organic Reactions

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