O-Chem Questions

[Myssey]

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I have a couple questions regarding O-chem. First, I will say that I am not good at O-chem. I am doing OK in my prep but there are a few things that just have not clicked yet and I am hoping that someone can explain them in simple......human terms.

1. What is steric hinderance exactly? Is the relative ease of the reaction taking place due to the absence/presence of bulky substituents?

2. What is the best way to rank the strength of a base/acid?

3. Are elimination reactions ONLY favored over substitutions when heat is applied?

I know that these questions may seem elementary but I do not have a good grasp on them and my test is coming up quickly. Please if you respond, explain it in simple terms and not in PhD terms....ha. I am actually scoring OK on this section but I feel that I could do much better if I had a firm grasp on these questions. Thanks in advance for your help!

 

[isquared]

Steric hindrance is the repulsion energy held in the bonds of atoms (near the electrophile), felt by the nucleophile as it makes it's attack.

Substitution reactions do not necessarily require heat. They are more dependent on the number of R groups around the electrophile, the ability of the leaving group to leave, the strength of the base/nucleophile, and the solvent.

Heat will help to speed up some slower reactions (Sn1), because the carbocation can be formed faster.

 

[isquared]

I just realized your question was about elimination reactions.

They do happen without applying heat, and the main factors are the substrate, the leaving group, and the base/nucleophile. (Bulky, or not?)

It's also important to remember that elimination reactions don't occur independently of substitution reactions. You will see products of both in a reaction, but one will dominate over the other depending on the above factors.