nucleophilic substitution reactions lab

[HLR03]

I am stuck writing a conclusion for this lab because I really didn't understand how mechanisms Sn1 and Sn2 relate to the lab. Can someone explain the purpose of the lab and whats going on?

 

-In the first part we did the synthesis: the preperation of tert-amyl chloride with 20 mL of 12M HCL and 12mL of t-amyl alcohol using a seperatory funnel and then a simple distillation. I am supposed to calculate the percent yield and have no idea how to. The weight of t-amyl chloride at the end was 5.66g?

 

-Second part was mechanism: relative reactivity of alkyl halides

I placed 4mL of 2% ethanolic silver nitrate solution in each of six test tube with 3 drops of a different alkyl halide in each and saw which formed a perciptate but what does it mean if it did form a pecipitate? How does it relate to Sn1?

[hypervalent_iodine]

A few things you need to know to work out % yield:

 

• How to convert from grams to moles. Do you know how to do this and by association, do you know how to calculate molar mass of t-amyl chloride?
• You will need to know how many grams of the t-amyl alcohol you had to be able to work out the number of moles of it; do you know how convert volume to mass? Hint: It has to do with density.

Once you work out how many moles of starting material (the alcohol) you have, you will need to work out how many moles of the chloride you would expect to get if 100% of the alcohol reacted. Working out the stoicheometry should be fairly straight forward; how many molecules of the alcohol do you need to make one molecule of your product? If it's 1 molecule of starting material for every molecule of product, that means (assuming 100% conversion) for every 1 mole of starting material you should, in theory, get 1 mole of product.

 

Theoretical yield is described as the mass of starting material you get assuming 100% conversion. Percent yield, which you need to calculate, is simply a an expression we use to describe what percentage of that you actually get after doing the experiment. Let's say, for instance, I have a reaction in which my theoretical yield is 1 gram. After doing the experiment, I only get 0.6 grams. My percent yield is found simply by dividing what I got by what I expected: 0.6 g / 1 g x 100% = 60%.

 

In regards to your second question, the important thing to note is what silver nitrate does when it reacts with an alkyl halide. Without giving too much away, you may find this bit from wiki useful. The precipitate you are seeing should tell you that some sort of reaction has taken place. No precipitate = no reaction. To understand why this is, you will need to look a little closer at how an S_N1 reaction occurs (i.e. the mechanism) compared to an S_N2 reaction. Before I start giving away the answer, can you tell me what you know about S_N1 vs. S_N2 reactions? Also, would you be able to list what the alkyl halides you used were and which ones you saw give a precipitate?

 

To get you started, think about the following reactions:

 

 

 

 

 

Of these, which do you think will most likely undergo an S_N1 type of reaction, which will undergo S_N2 and why?

Edited October 25, 2011 by hypervalent_iodine