Recently cognitive radio has been envisioned to solve the problem of spectrum scarcity and spectrum under-utilization. A cognitive radio performs communication by selecting a channel on an opportunistic basis. Thus the implementation of a cognitive radio for real-time application faces the challenge of sharing of a constantly varying sporadically available channel among multiple users. To this end we propose an energy efficient medium access control scheme for single-hop cognitive radio network (QCR-MAC) which provides four levels of QoS support with complexity equivalent to that of a single transceiver node. The scheme imparts QoS through the usage of different interframe spaces, which allows different priorities of winning a contention by packets from different applications. Two different channel access etiquettes are used according to the type of channel and data traffic. One spectrum etiquette favours stream based real-time data transfer while another favours bursty traffic. The protocol utilizes a beacon based structure for information interchange and thus allows contentions to be distributed on different channels whilst mitigating the control channel saturation problem. Simulation results shows the effectiveness of the proposed scheme over an existing similar work.