No puedo dormir si alguien ronca en la habitación de al lado.

Because dormir and dormirse are different.

• dormir = to sleep
• dormirse = to fall asleep

So:

• No puedo dormir = I can’t sleep
• No me puedo dormir = I can’t fall asleep

In your sentence, the idea is that the person is unable to sleep because of the noise, so dormir is the natural choice.

Puedo is the yo form of poder in the present tense.

• poder = to be able to / can
• puedo = I can

So No puedo dormir literally means I am not able to sleep, which in natural English is I can’t sleep.

Also note that poder is a stem-changing verb:

• yo puedo
• tú puedes
• él/ella puede

The o changes to ue.

Spanish often leaves out subject pronouns because the verb ending already shows who the subject is.

• No puedo dormir already clearly means I can’t sleep
• Adding yo is possible, but it usually adds emphasis:
  • Yo no puedo dormir... = I can’t sleep... / Me, I can’t sleep...

So the version without yo is the most neutral and natural.

Because this is a real, possible condition, so Spanish uses si + present indicative.

• si alguien ronca = if someone snores

Here, the speaker means a normal real-life situation: whenever that happens, they can’t sleep. That calls for the indicative, not the subjunctive.

Compare:

• Si alguien ronca, no puedo dormir. = If someone snores, I can’t sleep.
• Si alguien roncara / roncase... = If someone were to snore... / If someone snored...
  This sounds more hypothetical or literary.

So ronca is exactly what you expect here.

Ronca is the él/ella/usted form of the present tense of roncar.

• roncar = to snore
• alguien ronca = someone snores

Even though alguien means someone, it is grammatically singular, so the verb must also be singular:

• alguien ronca ✅
• alguien roncan ❌

Because alguien means someone / somebody, and grammatically it is singular.

So you say:

• alguien ronca = someone snores

not:

• alguien roncan

This is the same idea as in English: someone snores, not someone snore.

It means the room next door or the room next to this one.

The key part is de al lado, which means something like:

• next door
• adjacent
• beside this one

So:

• la habitación de al lado = the room next door

This is a very common Spanish expression.

Because when you use this expression to describe a noun directly, Spanish commonly uses de al lado.

• la habitación de al lado = the room next door
• el piso de al lado = the flat next door
• la casa de al lado = the house next door

By itself, al lado usually needs more structure, often with de after it:

• Está al lado de mi casa. = It’s next to my house.

So:

• la habitación de al lado ✅
• la habitación al lado ❌ or at least not natural in standard Spanish here

Al is the contraction of a + el.

• a + el = al

So historically:

• al lado = at the side

In modern Spanish, al lado is a fixed expression meaning next to / beside, and in de al lado it helps form the idea of the one next door.

Because en means in, and here the sentence means:

• if someone snores in the room next door

The snoring happens in that room, so en is the correct preposition.

• en la habitación = in the room

Using de la habitación would suggest something like of the room / from the room, which is not what is meant here.

Because the speaker is referring to a specific room: the room next door.

• la habitación de al lado = the room next door

Spanish often uses the definite article where English also uses the. In this sentence, it is a particular, identifiable room, so la is natural.

Yes, but the nuance changes a little.

• habitación = room; very common in Spain, especially for a bedroom or room in a house/hotel
• cuarto = room; common too, but depending on context it can sound a bit broader or more informal
• dormitorio = bedroom specifically

So these are possible:

• ...en la habitación de al lado = in the room next door
• ...en el cuarto de al lado = in the room next door
• ...en el dormitorio de al lado = in the bedroom next door

If you want the most neutral match for room, habitación works very well.

Yes. Spanish allows that word order easily.

• No puedo dormir si alguien ronca en la habitación de al lado.
• Si alguien ronca en la habitación de al lado, no puedo dormir.

Both are correct. The meaning is basically the same.

The difference is mainly emphasis:

• Starting with No puedo dormir... focuses first on the speaker’s problem.
• Starting with Si alguien ronca... sets up the condition first.

Sometimes, but the meaning changes slightly.

• si = if
• cuando = when / whenever

So:

• No puedo dormir si alguien ronca... = I can’t sleep if someone snores...
• No puedo dormir cuando alguien ronca... = I can’t sleep when/whenever someone snores...

In many real situations, both could work, but si presents it as a condition, while cuando sounds more like something that happens whenever that situation occurs.

Usually it sounds like a general truth or repeated situation.

• No puedo dormir si alguien ronca en la habitación de al lado.

This naturally suggests:

• Whenever that happens, I can’t sleep.

Spanish often uses the present tense for this kind of general statement, just like English does.

If you wanted one specific past situation, you would normally switch to past tenses.

Habitación is stressed on the last syllable: ha-bi-ta-CIÓN.

The written accent shows that stress.

Very roughly, in Spain Spanish pronunciation:

• ha = ah
• bi = bee
• ta = tah
• ción = thyon / syon depending on accent

In most of Spain, ci before a vowel is pronounced with a th sound:

• habitación ≈ ah-bee-tah-THYON

In many other Spanish-speaking areas, it sounds more like:

• ah-bee-tah-SYON

Both are standard in their own varieties.

Because in Spanish, no normally goes directly before the conjugated verb.

• No puedo dormir = I can’t sleep

That is the standard way to make a sentence negative.

Compare:

• Puedo dormir. = I can sleep.
• No puedo dormir. = I can’t sleep.

Not here, because alguien is the subject of the verb:

• alguien ronca = someone snores

The personal a is used when a person is a direct object:

• Veo a alguien. = I see someone.

So in your sentence, no a is needed before alguien.

Yes, it sounds natural in Spain Spanish.

A speaker from Spain would understand it immediately, and habitación de al lado is a normal way to say the room next door.

A few small alternatives are also natural, for example:

• No puedo dormir si alguien ronca en el cuarto de al lado.
• No puedo dormir si alguien está roncando en la habitación de al lado.

But your original sentence is perfectly good and idiomatic.