Question

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II. (8 pts.) Draw both possible chair conformations of the following compound as sawhorse projections. Show all substituents on the substituted positions of the ring. Each structure will be graded as right or wrong (no partial credit), so do your very best. OH

Answer 1

II. OH is cis to one Me group and trans to another Me group. For 1,2 substitutions, cis substituents lies aixial equatorial in chair conformation and trans substitutents lies in axial-axial and equatorial -equatorial positions.

III. For the first reaction, HCl reacts with the alkyne to give the more substituted product. Nucleophile attackd the more substituted stable carbocation.

For the second reaction, lindlar's catalyst is known for cis hydrogenation of alkynes. But here it is a terminal alkyne, So, there are no cis or trans forms. Then BH3 reacts to give the product. BH3 is attached to the less substituted end as among boron and hydrogen, hydrogen is more nucleophilic and has a partial negative character.  

Refer the image for more details.

О И WL Me Me Me HU room temps (leg.) 1 m Lindlar catalyst BH w