Q5. In the 1H NMR of 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy- $\beta$-Dglucopyranoside, the $\mathrm{H}-1$ proton appears as a doublet (d) at $\delta=5.46 \mathrm{ppm}$ ( $J=9 \mathrm{~Hz}$ ) while the $\mathrm{H}-2$ proton appears as a doublet of doublet (dd) at $\delta=$ $3.03 \mathrm{ppm}$ with $(j=9,10 \mathrm{~Hz})$. From these data determine which of the following chair conformations $\left({ }^{1} C_{4}\right.$ or $\left.{ }^{4} C^{1}\right)$ is adopted by the title compound and explain your answer.
$$
\begin{array}{l}
\| \rightarrow \delta=5.46 \
\|\| \rightarrow \delta=3.03
\end{array}
$$
$$
{ }^{1} \mathrm{C}_{4}
$$

The compound adopts the
${ }^{1} C_{4}$
conformation

Question

Q5. In the 1H NMR of 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy- $\beta$-Dglucopyranoside, the $\mathrm{H}-1$ proton appears as a doublet (d) at $\delta=5.46 \mathrm{ppm}$ ( $J=9 \mathrm{~Hz}$ ) while the $\mathrm{H}-2$ proton appears as a doublet of doublet (dd) at $\delta=$ $3.03 \mathrm{ppm}$ with $(j=9,10 \mathrm{~Hz})$. From these data determine which of the following chair conformations $\left({ }^{1} C_{4}\right.$ or $\left.{ }^{4} C^{1}\right)$ is adopted by the title compound and explain your answer.
$$
\begin{array}{l}
\| \rightarrow \delta=5.46 \
\|\| \rightarrow \delta=3.03
\end{array}
$$
$$
{ }^{1} \mathrm{C}_{4}
$$

The compound adopts the
${ }^{1} C_{4}$
conformation

Accepted Answer

∻Solution∻ ‖ 1 ⋮ **Analyze the NMR data for H-1**: The H-1 proton appears as a doublet at δ = 5.46 ppm with a coupling constant (J) of 9 Hz. This suggests that H-1 is coupled to only one neighboring proton with a relatively large coupling constant, indicative of a dihedral angle of about 60° between the coupled protons, which is typical for an axial-axial coupling in a chair conformation. ‖ ‖ 2 ⋮ **Analyze the NMR data for H-2**: The H-2 proton appears as a doublet of doublets at δ = 3.03 ppm with coupling constants J = 9 Hz and J = 10 Hz. This indicates that H-2 is coupled to two different protons with similar coupling constants, suggesting that H-2 is in an equatorial position, as axial-equatorial couplings are typically smaller than axial-axial couplings. ‖ ‖ 3 ⋮ **Determine the chair conformation**: Considering the coupling constants and the chemical shifts, the data suggest that H-1 is axial (due to the larger coupling constant) and H-2 is equatorial (due to the presence of two coupling constants). The ^1C_4 conformation would place H-1 in an equatorial position and H-2 in an axial position, which is inconsistent with the NMR data. Therefore, the ^4C_1 conformation is adopted by the compound, as it places H-1 in an axial position and H-2 in an equatorial position, consistent with the observed NMR data. ‖ ∻Answer∻ ⚹ The compound adopts the ^4C_1 conformation. ⚹ ∻Key Concept∻ ⚹ Coupling constants in NMR spectroscopy can help determine the spatial arrangement of protons in a molecule. ⚹ ∻Explanation∻ ⚹ The larger coupling constant for H-1 suggests an axial position, while the doublet of doublets for H-2 suggests an equatorial position. The ^4C_1 conformation is consistent with these observations. ⚹◊What is the significance of the coupling constant in NMR spectroscopy, specifically in the context of the provided proton signals in the 1H NMR spectrum?⍭ Generate me a similar question◊

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