Question

How do you diagram a compound sentence in which the two independent clauses are joined with a colon?

Answer 1

He thought that he could overcome all difficulties and arrive at a quick solution to the problem: that thought was dispelled when the situation turned from bad to worse.

Explanation:

The above is a compound sentence in which the two independent clauses are joined with a colon.

The independent clauses each consist of a noun and a verb at minimum. The sentence is compound because of the two clauses contained within.

But why? Why not just use two sentences?
The compound sentence has the benefit of urging the reader to digest all of the related information in one go, rather than breaking it up into pieces of information. This literary device establishes a flow in the prose.

Another way of writing the sentence (with less sarcasm) would be to use a conjunction and a comma to replace the colon:
He thought that he could overcome all difficulties and arrive at a quick solution to the problem, but that thought was dispelled when the situation turned from bad to worse.

This shows the diagraming of the compound sentence:
http://www.english-grammar-revolution.com/list-of-conjunctions.html