The discussion centers on the positive charge of the NAD+ molecule, specifically located on the nitrogen atom in the nicotinamide group. The nitrogen typically forms four bonds, raising questions about its charge since nitrogen has three valence electrons. The confusion arises from the assumption that this would lead to a negative charge. However, when examining the Lewis dot structure, it is noted that the nitrogen has a free lone pair of electrons before being protonated by H+, which contributes to the positive charge upon protonation. The formal charge on nitrogen is determined by considering all electrons in lone pairs and half of the bonding electrons. Thus, with four bonds (accounting for four electrons) and two inner shell electrons, nitrogen effectively has six electrons compared to its seven protons, resulting in a positive charge. The discussion clarifies that protonation does not leave an anion but rather results in a positively charged species.
