中(ちゅう)During, While, Throughout, In the process of

Both expressions refer to a continued state, but in different ways. うちに means 'do (B) while (A),' that is, during the ideal time or condition for (A), e.g. 熱いうちに食べてね ('Eat it while it's hot.') In contrast, 中 attaches to nouns and simply means 'during (A)' or 'in the middle of (A)', e.g. 会議中 ('in the middle of a meeting'), 授業中に携帯が鳴った ('My phone rang during class.')

Both patterns express being in the middle of an action, but differ in how they are used. 中 attaches to nouns to indicate 'in the process of' or 'during.' For example, 今、食事中です means 'I'm in the middle of eating.' ているあいだに refers to something happening while another action or state is ongoing. For example, ご飯を食べているあいだに電話が鳴った and 食事中に電話が鳴った are equivalent in meaning.

ながら attaches to verb stems to express performing one action simultaneously with another, e.g. 音楽を聴きながら勉強する 'listen to music while studying'. In contrast, 中 attaches to nouns to express 'while doing X,' and there is no requirement that what follows must be an action performed by the same subject, e.g. 会議中に電話がかかってきた ('A phone call came in while I was in a meeting.').

ているところだ and 中 are similar in that both express being in the middle of doing something, but they function differently grammatically. ているところだ is used with verbs, e.g. 今、食事をしているところです ('Now I'm in the middle of eating.'). In contrast, 中 attaches to the end of nouns and expresses a similar meaning, e.g. 今、食事中です, which means essentially the same thing but is more concise.

Both express a continued state or action, but are used differently. 中 attaches only to nouns and means 'in the middle of (A)', e.g. 会議中 ('in the middle of a meeting'), 使用中 ('in use'). の間に attaches to nouns (as-is), verbs/adjectives (with の removed), and な-adjectives (with な instead of の), and means 'while doing (A), (B)', e.g. 映画を観ている間に電話が鳴った ('While I was watching a movie, the phone rang.')

とき expresses the time of an action or event, like 'when' in English. It can be used with nouns as in 雨の時 'when it rains', verbs as in 父が帰ってきた時 'when Dad came home', or adjectives as in 暑い時 'when it's hot', and can describe one-time or repeated actions. 中 attaches to nouns and describes an action or state in progress, e.g. 勉強中 'now studying' or 使用中 'currently in use'.

Both express a continued state or action, but are used differently. 中 attaches only to nouns and means 'in the middle of (A)', e.g. 会議中 ('in the middle of a meeting'), 使用中 ('in use'). 最中に is used with verbs in the ている form or with nouns (using の) to mean 'right in the middle of (A), (B)', e.g. 食べている最中に話し掛けられた ('I was spoken to when I was right in the middle of eating.')