No. Whenever is convenient = At whatever time suits you Whenever it is convenient = At whatever time meeting up is convenient
(or whatever you want to get in for) In: "The shop is opened", "opened" is the past participle form of "open". This form (is opened) is used as the present simple passive. It focuses on the action of the store being opened; sometimes it is also said who opens it by using the preposition "by"... "The shop is opened by the owner's assistant."
Whatever obstacle is correct and means any obstacle, any at all. Whichever obstacle is also correct but the meaning is different - any of the already mentioned obstacles.
"Whatever" in its traditional sense, such as in "whatever you might think," or "whatever choice you make," is a totally different animal than this kind of teenage use that has spread everywhere and indicates a total dismissal of the line of discussion or the person.
The American Heritage Dictionary seems to allow both: Both whatever and what ever may be used in sentences such as Whatever (or What ever) made her say that? Critics have occasionally objected to the one-word form, but many respected writers have used it. The same is true of the forms whoever, whenever, wherever, and however.
If you go into a public library, you can borrow whatever you want - any book, or any of the videos or CDs if they have them. If you're given a choice of a dozen books, you can borrow whichever you like of that given group. Both words are correct there, but 'whichever' has more of a definite group in mind, whereas 'whatever' is more open.