2 orgo questions

[smile101]

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1)
If you have 2-chloro isopentane reacting in presence of KOH and alcohol, why would the reaction be E2 and not E1 (considering that its happening in the polar solvent)?

Is it E2 only because OH- is a strong base??

2) So Kaplan says that branching decreases the melting point because it can't pack well, while organic chm odyssey says that branching actually increases the MP because the crystal lattice could form better. Which one should I follow??????

 

[mddang]

1) Correct, -OH is a strong base.


2) Hmm...

Among branched chains of the same number of carbon atoms, more branching results in increased MP.

This doesn't mean that the branched alkane will always have a higher MP than the n-alkane.

 

[Hybridtavo]

Effect of branching on melting point more difficult to predict. For a given number of carbons, the more symmetric molecule will have the higher melting point

 

[klutzy1987]

1)
If you have 2-chloro isopentane reacting in presence of KOH and alcohol, why would the reaction be E2 and not E1 (considering that its happening in the polar solvent)?

Is it E2 only because OH- is a strong base??

2) So Kaplan says that branching decreases the melting point because it can't pack well, while organic chm odyssey says that branching actually increases the MP because the crystal lattice could form better. Which one should I follow??????

It depends on the size of the alkane as to what effect branching has on the melting point but if there is a disagreement between Dr. Romano and Kaplans i would go with Dr. Romano. The kaplans book is loaded with mistakes.

 

[visbimmer79]

Only undergo bimolecular reaction according to Solomon's text book!

SN2 Vs E2 is issue

It's already bulky, so elimination is favored with strong base!!

Unless primary, strong base is almost always E2!

If primary, only bulky stong base such as tertiary metoxy base causes E2!

-->Some text may say that strong base can cause E2 with primary alkyl halide! I conclude it's not true!!

By the way, only E2 can undergo Hofmann elimination!
E1 is always Zaitsev!

 

[A8]

1)
If you have 2-chloro isopentane reacting in presence of KOH and alcohol, why would the reaction be E2 and not E1 (considering that its happening in the polar solvent)?

Is it E2 only because OH- is a strong base??

2) So Kaplan says that branching decreases the melting point because it can't pack well, while organic chm odyssey says that branching actually increases the MP because the crystal lattice could form better. Which one should I follow??????

Strong bases such as KOH or NaOH favor E2.

 

[jay47]

Effect of branching on melting point more difficult to predict. For a given number of carbons, the more symmetric molecule will have the higher melting point

I agree with this statement, it is difficult to predict. However, for molecules with the SAME NUMBER OF CARBONS, the more symmetric the molecule ,the more easily it will pack together and the higher the MP.

I think that maybe you misunderstood what the other book meant. Why does a crystal lattice form from melting? I thought that it formed from solidifying, not melting.

I highly doubt you would see such a question on the DAT, it is too ambiguous. However, I would definitely know BP elevation, FP depression, and which molecule would boil at a lower temp type questions.

 

[bigstix808]

I think that maybe you misunderstood what the other book meant. Why does a crystal lattice form from melting? I thought that it formed from solidifying, not melting.

i think YOU might have misunderstood why the crystal lattice formation is relevant. you are correct in that during the process of solidifying, the lattice is formed. but why is that relevant, because during the process of MELTING (the topic at hand), that same lattice is broken. the more uniform the crystal lattice structre (as would result with symetrical branching, or saturated hydrocarbons), the higher the MP.