You probably already know that you can have a syllabic nasal instead of ən in words like button hidden Russian. But do you know where you can’t have a syllabic n?
One place where syllabic n is impossible in many accents of English, including General British English, is in words like London abandon mountain Camden. These words all have a nasal consonant followed by another consonant and then ən. Don’t turn the ən into a syllabic n.
Another place where syllabic n is not found is after l. So ən in fallen gallon swollen villain, please.