Ctrl-[ is the ASCII for Esc. Ctrl effectively subtracts 0x40. So:

    Ctrl-A = 0x41 - 0x40 = 0x01 = SOH
    Ctrl-I = 0x49 - 0x40 = 0x09 = Tab
    Ctrl-M = 0x4D - 0x40 = 0x0D = CR
    Ctrl-[ = 0x5B - 0x40 = 0x1B = Esc
    Ctrl-@ = 0x40 - 0x40 = 0x00 = NUL