Final answer:
An aldehyde's sp² hybridized C-H proton typically shows a downfield absorption in the 9.0-10.0 ppm range on an H NMR spectrum, due to deshielding by the adjoining carbonyl group's electronegativity.
Step-by-step explanation:
The sp2 hybridized C-H proton of an aldehyde generally absorbs in the 9.0-10.0 ppm range on a Hydrogen Nuclear Magnetic Resonance (H NMR) spectrum. The aldehyde hydrogen is deshielded due to the electronegativity of the adjoining carbonyl group, which increases its chemical shift. This shift is typically downfield compared to other types of hydrogens, such as those in alcohols or even aromatic protons.
An aldehyde's sp2 hybridized C-H proton exhibits this distinctive chemical shift because the carbonyl group's oxygen draws electron density away from the carbon-hydrogen bond, thus reducing the electron cloud around the hydrogen nucleus. This makes the nucleus more susceptible to the external magnetic field applied during NMR spectroscopy, thereby requiring a higher magnetic field (higher frequency) to achieve resonance, reflected as a larger chemical shift value.