Mr. Smith is the president of the corporation who will not accept our proposal
My professor holds that this is a good sentence, since who agrees with the subject, Mr. Smith. It sounds horrible to me.
Mr. Smith is the president of the corporation who will not accept our proposal.
Is this a good sentence?
The OP is right that it's a horrible sentence.
Consider some alternatives, starting with the original.
Mr. Smith is the president of the corporation who will not accept our proposal
The sentence as given is grammatical if it is interpreted to mean:
Mr. Smith is the corporation president who will not accept our proposal.
But it sounds more like an ungrammatical attempt to say:
Mr. Smith is the president of the corporation that will not accept our proposal
Since the original sentence is ambiguous, it would be a mistake to describe it as "good." It is a poorly written grammatical sentence.
Well, let's start with a rhetorical question. Would you consider the following to be a "good" English sentence?
Mr. Smith is the executive who will not accept our proposal.
I definitely consider this to be a "good" English sentence. It relies on the fact that there are multiple executives of which Mr. Smith is the one who's not impressed with the proposal.
Similarly, your sentence,
Mr. Smith is the president of the corporation who will not accept our proposal.
is a "good" English sentence if the following sentence holds true,
Mr. Smith is the president of the corporation, among all of the presidents of the corporation, who will not accept our proposal.
Fun sentence!
The disquiet here is because of the use of determiners with a preposition in the middle:
the president of the corporation
We expect the relative pronoun who to describe the noun that immediately precedes it. The sentence is grammatical if the president of the corporation is understood to be a noun phrase with president as the headword.
Writing the sentence as:
Mr. Smith is the president of the corporation that will not accept our proposal.
gives the corporation (and strips Smith of) agency, changing the meaning.
N.B. I've only given this a little thought, and would love to have problems with my logic pointed out, but this pattern (det n prep det n) isn't uncommon when it comes to titles:
- the head of the committee
- a man of the cloth
The first shows how changing the relative pronoun changes agency; the second can illustrate how important it is to recognize the first noun as the headword of the NP.
Sharon is the head of the committee who closed the deal.
is different to
Sharon is the head of the committee that closed the deal.
In the first case, Sharon did it; in the second, it was the committee. From this I'd argue that the OP's sentence is a grammatical construction that conveys a precise meaning.
Similarly,
Savonarola was a/the man of the cloth who was burned at the stake.
is grammatical.
Savonarola was a/the man of the cloth that was burned at the stake.
is also grammatical, but almost nonsensical as it sounds like Savonarola was made of cloth.