can i install quikbooks online in my iMac?

QuickBooks is a MS Windows only app. However you can install MS Windows on any Intel based iMac. There are two methods, the one I'd use is to purchase Parallels and then you can install MS Windows and Quickbooks and run both Windows and Mac OS simultaneously. The performance for Quickbooks should be excellent!!

The other method is, all Intel based Mac has Boot Camp installed. Boot Camp allows one to install MS Windows, which means you can boot into either Windows or Mac OS but not simultaneous. This is the least expensive but it is cumbersome.

You mentioned Quickbooks online, I am not familiar with that product if it is web based. If it is you should contact the developers of Quickbooks and ask..