[doublek1229]

Our teacher gave us sample data for the bromination of 3 compounds... anisole, analine, and acetanilide.  I know that they are all ortha-para directors and will add bromine... but how can I tell which is the most reactive and why?  It seems as though percent yield wise analine produced the most product followed by acetanilide, and lastly anisole.

Can someone explain this to me please!

[MissPhosgene]

Check your order again.

[doublek1229]

The teacher gave us sample data to compare to ours...

He had acetanilide 77 83 60 percent yield
analine 97 97 81 percent yield
anisole 58 88 52 percent yield

Then the melting point of the products.  So that is how I got my order?

[MissPhosgene]

If he wants you to judge reactivity by percent yield then you are right. However, I wouldn't do it that way but would refer to my textbook to see the order of activator strength.

[doublek1229]

According to the text book NH2 is the best activator followed by OCH3 and NHCOCH3.  So do you suggest in my report I talk about the high percent yield and then talk about which are the best ortho-para directors and how they are typically the most reactive?

[MissPhosgene]

I would do that. There are many ways to get erroneous yields... such as having solvent in the flask etc.

[Modestus]

I realize that we are now into the Fall semester and that this isn't of much help to you, but I would like to point out something to others seeking help for this question. I too am in an Organic Lab and we did an entire lab using those very compounds, the bromination of acetanilde, aniline, and anisole. You must trust you text book, because the reactivity is not directly linked to how much product you get, but rather what kind of product you get. It boils down to how many bromines are bonded to the ring and the position they take on the ring. For example, you can have five theoretical products for acetanilide (o-bromoacetanilide, p-bromoacetanilide, 2,4-dibromoacetanilide, 2,6-dibromoacetanilide, and 2,4,6-tribromoacetanilide) and each will have a corresponding melting point (99'C, 168'C, 145'C, 208'C, 232'C); in our class, it was experimentally determined that acetanilide will form p-bromoacetanilide. Which means that it is somewhat reactive. To really put it to scale, it's like this:
Position of the bromine      -      reactivity (1-5)
              o-                   -              1
              p-                   -              2
             2,4-                  -             3
             2,6-                 -              4
            2,4,6-                 -             5