Bonding in Lactams Is there Still a Role for Resonance

Bonding in Lactams Is There Still A Role for Resonance  

In collaboration with T. Darrah Thomas, Oregon State University, we employed gas-phase electron spectroscopy for chemical analysis (ESCA) to assess the nature of charge onN and O in distorted lactams [61a]. An earlier study ofN-ammonioimidates (solid state) found an excellent correlation between N u shifts and the carbonyl frequencies as predicted by resonance theory [62,63]. For l-azabicyclo[3.3. l]nonan-2-one (11), a low value for the ionization energy of Nu compared to the planar 1 -n-butylpyrrolidone (26) supports reduced positive charge on the nitrogen 

Proton Affinities of Bridgehead Bicydic Lactams N vs O Unstrained amides and lactams protonate and alkylate on oxygen. This is often explained through reference to resonance structures like 4C although the real point is the greatly enhanced resonance in O-protonated (alkylated) amides relative to the neutral amide [71], In contrast, 2-quinuclidones such as 10 protonate and alkylate on nitrogen since they are really ketoamines [32,33], 

Calculated 6-31G //6-31G proton affinities (kcal/mol) for N and O on bridgehead bicyclic lactams employing corrected zero-point vibrational energies and thermal factors (298 K) along with the 

Tjctam N-Proton Affinity O-Proton Affinity Difference Favoring N 

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