ashita wa kaigishitsu de douryou no tonari ni suwarimasu.

Tomorrow I will sit next to my coworker in the meeting room.

Breakdown of ashita wa kaigishitsu de douryou no tonari ni suwarimasu.

• は: topic particle
• の: possessive case particle
• で: location particle
• 明日あした: tomorrow

Questions & Answers about ashita wa kaigishitsu de douryou no tonari ni suwarimasu.

What does the particle は after 明日 do here? Can I just say 明日 without は?

• は marks the topic: it frames “as for tomorrow” and can add a mild contrast with other times (not yesterday, not today).
• Both are fine:
  • 明日は会議室で… sets tomorrow as the theme.
  • 明日、会議室で… simply states a time adverb; it feels a bit more neutral.
• Use は if you want to contrast or keep “tomorrow” as the ongoing topic in the conversation.

Can I say 明日に? When do I use に with time expressions?

• With adverbs like 今日, 明日, 昨日, 毎日, you normally omit に: 明日行きます.
• に is used with specific points in time: 3時に, 月曜日に, 1月1日に.
• 明日に is generally unnatural in this kind of sentence. It can appear in set phrases or special nuances:
  • 明日にする “let’s make it tomorrow” (deciding a deadline/appointment)
  • 明日には… to add contrast/emphasis or “by tomorrow at least”

Why is 会議室 marked with で and not に?

• で marks the place where an action occurs: 会議室で話す “talk in the conference room.”
• に marks destination or existence: 会議室に行く “go to the conference room”; 会議室にいる “be in the conference room.”
• With 座る, に marks the target surface/spot (椅子に座る “sit on a chair”), while で marks the broader location of the action (会議室で座る “do the act of sitting in the conference room”). Your sentence is correct.

Why is it 同僚のとなり and not 同僚となり?

• の links nouns. X の となり means “the next-to-X position,” literally “X’s next (spot).”
• となり is a noun, so it needs の to attach to another noun: 同僚のとなり, 先生のとなり, 駅のとなり, etc.