can any one tell me how the distance between the oxygen atom joined to the ring and the -OH group of the carboxylic acid in aspirin ... can relieve pain?

Question

For example what would be the effect of increasing the distance ?

Here is a LONG discussion of aspirin, much of it unrelated to your question. However, if you will scroll to the section on "mechanism of action" there is a discussion that may be of benefit to you. http://en.wikipedia.org/wiki/Aspirin

Here is a LONG discussion of aspirin, much of it unrelated to your question. However, if you will scroll to the section on "mechanism of action" there is a discussion that may be of benefit to you.