Page 35 of my textbook, Mass Spectrometry by Jürgen H. Gross, says the following in a section on ionization energy (IE) and charge localization:
Molecules with π-bonds have lower IEs than those without, causing the IE of ethene to be lower than that of ethane. Again the IE is reduced further with increasing size of the alkene. Aromatic hydrocarbons can stabalize a single charge even better and expanding π-systems also help making ionization easier.
My questions are as follows:
Why do molecules with π-bonds have lower IEs than those without?
Why does expanding π-systems help making ionization easier?
I would greatly appreciate it if people could please take the time to clarify this.