TBR Orgo Ch 1 - Q50 in 52Q set

[Sarvish]

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The answer says "Esters have no lone pair of electrons that can be readily donated to a proton". Doesn't the oxygen on the carbonyl have 2 lone pairs?

Dealing with the same question, why is nitrogen more basic than oxygen and sulfur? It's EN falls in between both elements which rules that out as a reason and I can't think of any other explanation

 

[Like]

The carbonyl group in an ester does have two lone pairs of electrons but they can't be donated possibly because the OR group is electron withdrawing. Who really knows? It's based on observation that the two lone pairs of electrons do not participate in reactions.

Electronegativity is how well an atom attracts electrons, but you're talking about attracting protons (basicity). Nitrogen is right next to carbon which likes to have four bonds and nitrogen slightly displays this tendency as well. As you move more to the right, the atoms get more stable and like to have less bonds (until you get to the noble gases, which usually don't have any bonds). A thing to think about is that oxygen has more protons (and neutrons) than nitrogen, which makes the nucleus somewhat more positive. This in return, pulls the electrons closer to the center (atom radius decreases), so the lone pair of electrons form less stable bonds (they won't hold on to a proton as strongly as nitrogen's lone pair would). Again, all observation of the physical world.

 

[AureatEagle]

The carbonyl group in an ester does have two lone pairs of electrons but they can't be donated possibly because the OR group is electron withdrawing. Who really knows? It's based on observation that the two lone pairs of electrons do not participate in reactions.

Electronegativity is how well an atom attracts electrons, but you're talking about attracting protons (basicity). Nitrogen is right next to carbon which likes to have four bonds and nitrogen slightly displays this tendency as well. As you move more to the right, the atoms get more stable and like to have less bonds (until you get to the noble gases, which usually don't have any bonds). A thing to think about is that oxygen has more protons (and neutrons) than nitrogen, which makes the nucleus somewhat more positive. This in return, pulls the electrons closer to the center (atom radius decreases), so the lone pair of electrons form less stable bonds (they won't hold on to a proton as strongly as nitrogen's lone pair would). Again, all observation of the physical world.

The OR group is actually electron donating. The answer provided by the textbook is factually incorrect. By resonance, the OR group donates one of its lone pairs into the carbonyl such that the carbonyl O ends up with a formal negative, and the O in OR ends up with a positive. The OR group O is not basic at all because of this resonance structure (its lone pair is delocalized, and it has a slight positive charge, making it non-nucleophilic). The carbonyl O, however, is delta - by resonance and certainly basic enough to grab a proton. Your textbook is either making a simplification, or it's answer is taken out of context of the actual question.

 

[Romz]

The OR group is actually electron donating. The answer provided by the textbook is factually incorrect. By resonance, the OR group donates one of its lone pairs into the carbonyl such that the carbonyl O ends up with a formal negative, and the O in OR ends up with a positive. The OR group O is not basic at all because of this resonance structure (its lone pair is delocalized, and it has a slight positive charge, making it non-nucleophilic). The carbonyl O, however, is delta - by resonance and certainly basic enough to grab a proton. Your textbook is either making a simplification, or it's answer is taken out of context of the actual question.

Exactly what I thought.

I thought about N in really basic terms. It has a lone pair of electrons when in NH3 form and can undergo a coordinate covalent bond to become NH4. Can Oxygen do that? NOPE! Oxygen is a lot more greedy with it's electrons and as a result a lot less likely to give them up as N does.

Hope that helps! 🙂