2) The aromatic region of the H-NMR spectrum of pyridine is provided below. Assi

Question

2) The aromatic region of the H-NMR spectrum of pyridine is provided below. Assign each of the H-NMR signals to their corresponding H-atoms in pyridine. Draw a series of resonance structures that justify the observed chemical shifts and the NPA charges shown below determined by a B3LYP/6-31G(d) NBO calculation. 2) The aromatic region of the 'H-NMR spectrum of pyridine is provided below. Assign each of the "H-NMR signals to their corresponding 'H-atoms in pyridine. Draw a series of resonance structures that justify the observed chemical shifts and the NPA charges shown below determined by a B3LYP/6-31G(d) NBO calculation. Ha Ha 2(2) 72 7 78 27 75 24 +0.24 +0.22 +0.02 0.28 -0.45 0.20-+0.24 +0.02 -0.28 +0.22 +0.24 LP( 1 )N6 s(2912%)p2.43(70.72%) 3) Based upon your resonance structures, the observed H-NMR chemical shifts, the NPA atomic charges, and the hybridization and image of the N-atom lone pair shown above, what can you conclude about the ability of the lone pair to conjugate with the aromatic syst Explain in detail. em?

Explanation / Answer

The peak at 4.15 ppm belongs to the protons in ferrocene. Due to the five-fold symmetry of the cyclopentadienyl rings, the protons are all chemically equivalent, hence there is only one signal. The rapid rotation of the rings around the Fe centre results in the rapid equilibration of the protons in ferrocene. Furthermore, there are no neighbouring protons to couple with thus the signal is a singlet. The chemical shift value of 4.15 ppm is lower than that for aromatic protons at 7 ppm because there is an increased electron density in the two rings that increases the shielding effect, causing a decrease in the chemical shift value.

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