C# Dominant #11

C# Dominant #11, written C#7#11, is built from C#, E#, G#, B and G: the root, major 3rd, 5th, minor 7th and sharp 11th.

Its 3rd and 7th, E# and B, are its guide tones: they say what kind of chord it is, so voicings are built around them and the root is often left to the bass. G7, a tritone away, has the same two notes the other way up, so it can stand in for C#7#11 as its tritone substitute.