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- Stereochemistry - Workbook: 191 Problems and Solutions
- Chiral Drugs: An Overview
- GRE Subject Test: Chemistry : Stereochemistry
- 4.E: Solutions to Stereochemistry, Conformation, and Configuration Problems
Both compounds are 4-ethylmethylhexane. Therefore, they are identical compounds. The first compound is 2,3,5-trimethylheptane, and the second is 3-ethyl-2,5-dimethylhexane.
Stereochemistry - Workbook: 191 Problems and Solutions
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Figure 1. Representational translation from 2D structures to Newman projections and chair conformations, with common student errors.
Figure 2. Cahn—Ingold—Prelog process to assign R and S stereocenters, including common errors represented with dashed arrows. Figure 3. Partial screenshots of the Cahn—Ingold—Prelog and Newman projection web-based tools. Both resources have computer models linked to the 2D structures and use drag and drop features to answer the problem. Figure 4. Partial screenshots of the chair conformation tool before and after an attempt to solve the representational translation.
More by Nimesh Mistry. More by Ravi Singh. More by Jamie Ridley. Cite this: J. Article Views Altmetric -. Citations 2. Abstract High Resolution Image. Stereochemistry forms a fundamental part of most, if not all, organic chemistry courses.
It plays a vital role in our understanding of molecular structure, reactivity, and our ability to synthesize molecules of biological importance.
This is a process known as representational translation. Recently, we performed some detailed analysis of the types of errors students make when drawing Newman projections from 2D dashed—wedged structures. The most common errors were incorrectly drawing the orientation of the three groups around either carbon, thus switching the stereochemistry of the molecule, or having the carbons which should be at the front and rear of the Newman projection the wrong way round Figure 1.
When students were asked to draw 2D dashed—wedged structures from Newman projections, stereochemistry featured as the most common error. When students were drawing chair conformations, the most common error was positioning substituents incorrectly in incorrect axial or equatorial positions, which is also switches the stereochemistry.
Another common error was changing the orientation of two substituents around the chair from what was given in the 2D structure. When assigning R and S labels to stereocenters, common student errors included viewing the lowest-priority group coming toward the observer, or mixing up if a clockwise or anticlockwise a synonym for counterclockwise in the UK rotation is assigned to R or S Figure 2.
High Resolution Image. Perhaps the most common advice given to students is to use molecular models to help them perform these types of tasks. Molecular models are thought to aid students by off-loading the cognitive burden of visualizing a molecule in three dimensions, help students develop more complete mental models, and help students relate 3D and 2D representations. Web-Based Stereochemistry Tools.
The aim of this work was to develop resources that students could use to improve their ability to translate 2D dashed—wedged structures to Newman projections and chair conformations, as well as assign R and S labels to stereocenters correctly.
Virtual models were provided, and these models were connected to the 2D structures in the problems. These resources break down the components of each type of stereochemistry problem for students to see which parts of the problem they are solving correctly and incorrectly. General Features. The desire was to ensure these resources were as accessible to students as possible, which meant being operational on computers, tablets, and mobile devices.
To achieve this, all resources are web-based and open-access from University of Leeds servers. The Newman projection and CIP tool can be accessed from the same website, 34 while the chair conformation tool is accessed from a different website due to some of its unique features. Each tool includes a virtual 3D model, and its corresponding 2D dashed—wedged structure that is linked together.
Students can move, rotate, and zoom in or out with these structures to view them from different perspectives as they would be able to do with a physical model. The Newman projection and CIP tools have been designed so that when an atom or bond in the 3D structure is selected, the same part of the 2D structure is simultaneously highlighted. In the chair conformation tool, both the 2D and 3D structures are numbered to help develop mapping strategies.
Each resource contains problems with different levels of difficulty. Students start with the level that reflects their ability and move to a higher level when they are ready. This reflects the need for students to ultimately become able to perform these mental rotations without a 3D model.
For both the CIP and chair conformation tools, the complexity of the molecules with which students deal with also increases with the higher levels. All resources contain a feature highlighting which parts have been answered correctly, in green, or incorrectly in red. If students make errors, they can focus on the aspects that need improving to achieve the correct answer. When students select a level in the CIP tool, they are given a 2D and 3D structure of the same molecule generated at random.
On the Easy level, known drug molecules are used which contain only one stereocenter Figure 3. On the Medium level, natural products and drugs with multiple stereocenters are used. A particular carbon in the molecule is highlighted in orange, which indicates that it is the stereocenter and is the one which needs to be assigned R or S. The surrounding atoms are also labeled for the prioritization step. Students drag and drop the boxes representing atoms around the stereogenic carbon into the order of their prioritization.
They then select the orientation of the highest-priority groups to be clockwise or anticlockwise, with the option of using the 3D model to help them do so and finally select the assignment to be R or S. Both the rotation and assignment sections have a white box that slides toward the option selected by the student. When the answer is submitted, the correct green and incorrect red parts of the answer become highlighted.
The students can then revisit the rules and use the 3D model to observe how the correct orientation is achieved by looking from the correct perspective. Students have the opportunity to correct and resubmit their answers again until they are fully correct.
Newman Projection Tool. The Newman projection tool helps students translate from 2D dashed—wedged structures to Newman projections or vice versa. Students can select which type of translation they wish to perform. For both types of problems, students are given a structure at random with six different substituents around the two respective carbons and an eye indicating the perspective for constructing the correct Newman projection or 2D structure Figure 3.
The accompanying 3D model has the substituents in the same position as the 2D structure. Students can use the 3D model to perform the rotation that occurs when a dashed—wedged structure is rotated to view the same molecule along its carbon—carbon bond or vice versa and see how the substituents orient themselves in this process. Problems requiring a Newman projection from a 2D dashed—wedged structure have a staggered conformation with vacant boxes for the substituents to be placed in.
Similarly, a 2D dashed—wedged structure with vacant boxes is given in the Newman projection to 2D problems. In both cases, students perform the correct translation by placing the substituents where they think they should be in the Newman projection or 2D structure, respectively. The correct green and incorrect red parts of the translation are highlighted when students submit their answer.
Common errors such as switching the stereochemistry of a carbon will become highlighted; therefore, students can focus on the parts of the translation where they are weaker to improve.
Chair Conformation Tool. For the chair conformation tool, students translate 2D dashed—wedged structures to chairs by constructing a virtual substituted cyclohexane that matches the 2D structure. To start with, students are given two 3D models of cyclohexane with each carbon in the ring numbered to match the 2D structure Figure 4.
The two 3D structures are also ring-flipped conformers. To construct the correct chair models, students are given a menu with five different functional groups.
When they drag and drop a functional group over a hydrogen in the 3D model, it will exchange the hydrogen for the functional group. This feature helps students to match the stereochemistry of a functional group in the chair from a 2D structure and also consider if it should be axial or equatorial.
The numbering helps to ensure students can learn how to place substituents around the ring relative to each other. This strategy is known as mapping and has been used successfully in the teaching of curved arrow mechanisms. When students check their answers, each 3D model shows if it is correct green or incorrect red. As with the other tools, students can correct their errors and resubmit their answers. When the students have achieved both correct chairs, they will be given both chair structures in the standard line diagram format.
They then select which chair is the more stable to complete the problem. Stereochemistry is taught to Chemistry, Medicinal Chemistry, and Natural Science students as part of a 10 credit semester 2 module in year 2. Students are introduced to Cahn—Ingold—Prelog rules, Newman projections, and chair conformations as part of the course. The module typically has — students enrolled each year. Links to the resources were incorporated into lecture notes as QR codes. The lecturer used these resources to show students how to answer these types of problems.
Students were given the opportunity to use them to answer problems in the lectures. Anonymous module evaluations are used by the institution for each module. This includes a section where students can comment on what they found positive about the course.
This was a useful indication for determining that students found value from using these resources and were engaging with them. Student engagement with the resources was also determined from the web usage statistics using Google analytics Figure 5. Throughout the course there was low-level usage of the resource with minor spikes when the resource was introduced in lectures and for the associated tutorial.
Chiral Drugs: An Overview
It seems that you're in Germany. We have a dedicated site for Germany. The late Edgar Heilbronner, one of the great physical and organic chemists of the 20th century, had a particularly effective lecture. He started it as follows: "You know pretty much everything I am going to say. So let us begin with the questions.
Stereochemistry. Pages·· MB·5, Downloads. The chirality (or handedness) at stereogenic centers is specified by application of the Cahn-Ingold-.
GRE Subject Test: Chemistry : Stereochemistry
The molecules in this problem are isomers because they each have unique configurations and do not share the same funcitonal groups at the same carbon positions. Enantiomers are reflections of each other. Geometric isomers are compounds that have the same molecular formula but they differ in the way they are arranged spatially.
The key to mastering chirality and stereochemistry is through practice, practice, and more practice. But where do you get all those practice problems? Determine if the following molecules are optically active chiral or optically inactive achiral. Rank each set of substituents from high to low priority using Cahn-Ingold-Prelog ranking rules. Hint: Need help ranking?
Although they have the same chemical structure, most isomers of chiral drugs exhibit marked differences in biological activities such as pharmacology, toxicology, pharmacokinetics, metabolism etc. Some mechanisms of these properties are also explained. Therefore, it is important to promote the chiral separation and analysis of racemic drugs in pharmaceutical industry as well as in clinic in order to eliminate the unwanted isomer from the preparation and to find an optimal treatment and a right therapeutic control for the patient. In this article, we review the nomenclature, pharmacology, toxicology, pharmacokinetics, metabolism etc of some usual chiral drugs as well as their mechanisms. Different techniques used for the chiral separation in pharmaceutical industry as well as in clinical analyses are also examined.
Orient the following so that the least priority 4 atom is paced behind, then assign stereochemistry R or S. Draw R bromobutanol. The stereo center is R.
4.E: Solutions to Stereochemistry, Conformation, and Configuration Problems
Затаив дыхание, она вглядывалась в экран. КОД ОШИБКИ 22 Сьюзан вздохнула с облегчением. Это была хорошая весть: проверка показала код ошибки, и это означало, что Следопыт исправен. Вероятно, он отключился в результате какой-то внешней аномалии, которая не должна повториться. Код ошибки 22. Она попыталась вспомнить, что это. Сбои техники в Третьем узле были такой редкостью, что номера ошибок в ее памяти не задерживалось.
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В эпоху Возрождения скульпторы, оставляя изъяны при обработке дорогого мрамора, заделывали их с помощью сеrа, то есть воска. Статуя без изъянов, которую не нужно было подправлять, называлась скульптурой sin cera, иными словами - без воска. С течением времени это выражение стало означать нечто честное, правдивое. Английское слово sincere, означающее все правдивое и искреннее, произошло от испанского sin сега - без воска.
Странно, - удивленно заметил Смит. - Обычно травматическая капсула не убивает так. Иногда даже, если жертва внушительной комплекции, она не убивает вовсе. - У него было больное сердце, - сказал Фонтейн.
Мужчины начали спорить.