# Is the lone electron pair of an amide nitrogen part of the π system when building a Hückel matrix?

Is the lone electron pair of the nitrogen atom part of the conjugated π system in the α,β-unsaturated amide pictured below?

Is there a general rule for choosing when to include a nitrogen atom in a Hückel matrix?

• I have edited your post for clarity. At the risk of incurring ill-will from our German folks, I have replaced your "ue" (yes, it's correct; no, most people don't know that) in the title and added back the umlaut in the text. Jul 15, 2021 at 23:14
• Pro tip: get to know a compose key and never fear Unicode German or Greek letters again with simple and intuitive keystrokes like RAlt " u for letter ü or RAlt * p for letter π (cc @ToddMinehardt). Jul 15, 2021 at 23:22
• @ToddMinehardt So to get it right - is or is not ue acceptable EN transcription for DE ü ? ( I guess such transcriptions would get hard time for CZ ones ) // An alternative is to have a short list of frequent UC characters and codes, performing either copy/paste either invoking unicode insertion by the code, like CTRL+SHIFT+U<unicode>ENTER on Linux. Jul 16, 2021 at 8:54
• Actually I am German, so I have the ü right on my keyboard. I have just always read the "ue" spelling in English literature, so I thought I'd not confuse you with umlauts :D Jul 16, 2021 at 9:12
• I guess you can include the lone pair in the Huckel matrix, but it will probably become very difficult to solve by hand. If you have a computer, that will solve it. If you ignore the lone pair, your system is only a linear chain of p-orbitals, it will give that diagonal looking matrix (not a diagonal matrix!!) that you could solve with a pen and paper. Jul 16, 2021 at 10:41