Learn Swedish: Vi stannade vid huvudentrén, framför vilken vaktmästaren väntade. - We stopped at the main entrance, in front of which the caretaker was waiting.

While som is the most common relative pronoun in Swedish, you cannot place a preposition directly in front of it. To write 'in front of which', you must use a preposition followed by vilken (for en-words) or vilket (for ett-words). Because huvudentré is an en-word, we use vilken.

Could I rewrite this sentence using som?

Yes, but you would have to move the preposition to the end of the relative clause: Vi stannade vid huvudentrén, som vaktmästaren väntade framför. The version with framför vilken is much more formal and mostly used in writing.

Why is the subject vaktmästaren placed before the verb väntade in the second part of the sentence? Doesn't Swedish use V2 word order?

The V2 (verb-second) rule applies to main clauses. The phrase starting with framför vilken is a subordinate relative clause, so it uses standard subordinate clause word order: subject (vaktmästaren) followed by the verb (väntade).

huvud is an ett-word, so why does huvudentrén end with an en-word definite suffix?