How to benefit the most from this exercise: visualizing a molecule in 3D perspec

Question

How to benefit the most from this exercise: visualizing a molecule in 3D perspective from ID representation is a daunting task. These questions are designed to strengthen your spatial intelligence, not meant to be regular exam questions. The suggested way to use these questions is to build the model, take mental snapshots from different angles, answer questions, and then try to reproduce the 3D shape of the molecule without the model. This will foster the ability to visualize molecules given in ID representation in 3D space. The (+) enantiomer of a compound displayed an observed optical rotation of -1.72degree when measured in a polarimeter with a 1 dm pathlength of light at a concentration of 0.02 g/mL. Calculate the specific rotation for the (-) enantiomer of this compound. Build the following molecules with the model kit and assign R/S configuration to all chiral centers. Then determine the absolute configuration without relying on the model and write R or S with an arrow pointing to the corresponding chiral center. Build two 2-chlorobutane molecules as shown below. Make sure A and B are not superimposable. What is the stereochemical relationship between A and B:___(choose from enantiomers, diastereomers, identical, or others) Take model A and switch any two substituents on the chiral center. Now, what is the stereochemical relationship between A and B:___(choose from enantiomers, diastereomers, identical, or others). Keep in mind: switching any two substituents on the chiral center results in the opposite configuration, therefore leading to the mirror image or enantiomer. Complete the partial Fisher projections below:

Explanation / Answer

1 enantiomers

2 identical

3 For A (H to the left, Cl to the right)

For B (Cl to the left, H to the right)

4. It is B, if you rotate the Cl, CH3 and H one position clockiwise you'll get the same as above

4)

1.

A) (2S,3R)-2,3-dichlorobuthane

B) (2R,3R)-2,3-dichlorobuthane

C) (2S,3S)-2,3-dichlorobuthane

D) (2R,3S)-2,3-dichlorobuthane

2. B and C are achiral, since you can overlap the same functional grupo

3.

A and B diasteromers

A and C diasteromers

A and D enantiomers

B and C identical

B and D diasteromers

C and D diasteromers

5.

1) (1S,2R) for A and (1S,2R) for B

2) identical

3)both are achiral, because they have a symetry plane

4) 3 constitutional isomers, none of them would have optic activity

6.

1) A is (1R,2R) B is (1S,2R)

2)Enantiomers

3) yes and yes, A is dextrorotatory and B is levorotatory

4)3 and 1 of the rotate polarized light

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