Apex domains cannot have CNAME records.
Question and response
Question
dig thomasmobrien.com. NS
Answer
thomasmobrien.com. 2 NS ns-1640.awsdns-13.co.uk.
thomasmobrien.com. 2 NS ns-1542.awsdns-00.co.uk.
thomasmobrien.com. 2 NS ns-989.awsdns-59.net.
thomasmobrien.com. 2 NS ns-1695.awsdns-19.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0