Q: Imac blue tooth fails pairing with iphone 5c

The iPhone has a very limited list of supported bluetooth profiles: http://support.apple.com/kb/HT3647

It will only pair with an iMac (or any computer) for tethering (personal hotspot) and that is only possible if your carrier supports it. If that is why you are trying to pair with the iMac and it is not working, the following may help: http://support.apple.com/kb/TS2756