Treatment of a carboxylic acid with trifluoroacetic anhydride leads to an unsymmetrical anhydride that rapidly reacts with alcohol to give an ester. Using the reaction of acetic acid as an example, propose a structure for the first intermediate in the reaction to form the unsymmetrical anhydride.

The first intermediate is protonated form of trifluoroacetic anhydride.

Explanation:

The first step in the formation of unsymmetrical anhydride is the protonation of carbonyl oxygen atom.

Here acetic acid donates its proton to carbonyl oxygen of trifluoroacetic anhydride because the carbonyl oxygen has partial negative charge in its resonance hybrid.

So, the first intermediate is protonated form of trifluoroacetic anhydride.

Structure of the 1st intermediate has been given below.

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.