Incase of alkyne, value of chemical shift should be more than alkene according to electronegativity but it is been found experimentally that in case of alkenes it is more and the reason is given by anisotropy.If we keep the molecule in horizontal direction protons of alkyne will come in deshielded region which means more chemical shift value which is not the case found experimentally.So it is considered that alkyne remains in vertical upright position for maximum of time due to which protons come in shielded region and value of chemical shift comes out to be less than alkenes.Hope this helps.
For acetaldehyde, the π-electron cloud is oriented perpendicular to the applied magnetic field, resulting in a diamagnetic effect and lower chemical shift. For ethyne, the π-electron cloud is aligned parallel to the applied magnetic field, leading to a paramagnetic effect and higher chemical shift.
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I thought the resonant magnetic field strength is inversely proportional to the chemical shift? Why Bnet of C2H2 lower then the chemical shift also be lower too?
