Test: Stereochemistry Level - 1

Diastereomers have different physical properties. They can be separated by ordinary separation techniques such as fractional crystallization.

Gauche and anti-conformers are stereoisomers not related by mirror-image relationship, hence diastereomers.

• Fully eclipsed conformation: the rotation of the gauge conformation to 60 degrees results in the gauge conformation and it is the least stable conformation of all.
• Hence, the most stable conformation of ethylene glycol is gauche conformation.

• Eclipsed atoms are not valid in boat configurations.

• Flagpole interaction generally raises the strain and then energy in cyclohexane (boat conformational structure).
• You can imagine this as two hydrogen atoms at pole position (1, 4) and the interaction between them.
• The boat conformations have higher energy than the chair conformations. The interaction between the two flagpole hydrogen atoms, in particular, generates steric strain.
• Torsional strain also exists between the C2–C3 and C5–C6 bonds, which are eclipsed. Because of this strain, the boat configuration is unstable (i.e. is not a local energy minimum).

Hence D is correct.

• The reaction in which stereochemically different molecules react differently is called stereospecific reaction.
• Stereospecificity is the property of a reaction mechanism that lead to different stereoisomeric reaction products from different stereoisomeric reactants, or which operates on only one of the stereoisomers.

• There is a possibility of Hydrogen Bonding between "Hydrogen(H)" of OH group and "Oxygen(O)" of OMe group. 
• So if they are oriented in such a way that these two groups are close to each other , the strength of hydrogen bond would increase making it more stronger.
• Hence, Option A, because of Hydrogen Bonding becomes the most stable isomer. 

Louis Pasteur was the first documented person to separate stereoisomers.

• The above reaction is an example of E2 elimination.
• For E2 elimination both the leaving group must be anti w.r.t each other in the adjacent carbon atoms.
• In option C, we get this requirement of anti geometry of the Br atoms, so it undergoes reaction. 
   

Both molecules have the same molecular formula (C9H16BrCl) and the same connectivity. Each molecule also has three stereocenters, marked above with an asterisk, and does not contain a plane of symmetry. Therefore, both molecules are chiral. Using one of the methods outlined in this tutorial, it can be determined that these molecules are superimposable. Therefore, the molecules are identical.

The two substituents in the cis 1,4-disubstituted chair cyclohexane shown are necessarily axial and equatorial, as in (a), (b) and (d). In (c), however, the 1,4-substituents are both equatorial so this is the trans isomer, i.e. a different compound.

In identifying stereogenic centers, any quaternary or tertiary carbons would be a good place to look. There are no quaternary carbons, and all the tertiary carbons are part of a benzene ring structure.