What is the function of "al" in this question?
One of my homework questions reads "¿Qué hace José al entrar en la clínica?" I'm pretty sure a loose translation would be "What does José do upon entering the clinic?" and I know how to answer it. What I don't understand is the function of "al" before "entrar." As far as I know "al" is a contraction of "a" and "el" and means "to the." But why would you need "to the" in that sentence? (My teacher is a native Venezuelan, so I can't assume it's bad Spanish.) Translators and dictionaries haven't yielded an answer.
3 Answers
Here:
http://spanish.about.com/od/sentencestructure/qt/al_infinitive.htm
The use of the contraction al followed by an infinitive is a very common way of indicating when something happens.
Al followed by an infinitive is usually the approximate equivalent of "upon," "on" or "when" followed by the gerund (the "-ing" form of a verb) in English.
Here are some examples of this usage:
El diagnóstico se hace al encontrar que hay dolor. (The diagnosis is done upon finding that there is pain.)
Hay error al enviar mensajes desde mi programa de correo. (There is an error when sending messages from my email program.)
Lea en la mañana al despertarse; lea en la noche al acostarse. (Read in the morning on getting up; read in the evening when going to bed.)
Al comprar una empresa, la consideración más importante es sus aspectos económicos. (When buying a business, the most important consideration is its economic aspects.)
Me puse nervioso al ver la osa con su crías. (I became nervous upon seeing the bear with her cubs.)
Al escuchar el himno nacional todas las personas quitarán el sombrero. (On hearing the national anthem, all the people will take off their hats.)
The translations given above are fairly literal. If you were translating such sentences in real life, you'd probably rephrase in some cases in order to get more natural English:
Hay error al enviar mensajes desde mi programa de correo. (I get an error when I send messages from my email program.)
Me puse nervioso al ver la osa con su crías. (I became nervous when I saw the bear with her cubs.)
Keep in mind that although the infinitive used as a noun is frequently encountered bare, it can take an article, and that article is always "el".
Another link:
nos confundimos al hablar sin escuchar
Most native English speakers would find the phrase simpler to follow if Daniel had avoided the al + infinitive construction and instead sung Nos confundimos cuando hablamos sin escuchar or Nos confundimos hablando sin eschuchar, both more parallel to typical English construction. Each of these possibilities is grammatically correct, but they convey a slightly different meaning than that which is attained by the lyric's use of al hablar. Both hablando (speaking) and cuando hablamos (when we speak), would convey the sense that He is referring to some specific instance or instances of "talking without listening," whereas the use of al hablar makes the overall statement sound more like a truism, a principle of life, the type of thing you might read at the end of a fable or as the moral of the story.
We don't do your homework for you!! 
I believe that the "a" and "el" are used because in that sentence, "entrar" or "el entrar" is used as a noun. Trying to force it into an English way of speaking, you could think of it as "upon the entering into the clinic."
But I will certainly defer to those more knowledgeable.
upon - al or when. Que hace cuando entre la clínica?
