Vinylic Protons Are Acidic Because

Protons c is bonded to an sp2 carbon which makes it a poor acid.

Vinylic protons are acidic because.

A better question would be what s an allylic position because allylic proton is nothing more than proton hydrogen in allylic position. The book indicates the red proton is the more acidic proton. If so then this explains why the red proton is more acidic because it has a delocalized pair of electrons while the blue proton does not have a delocalized pair of electrons. Notice that the proton closest to the carbonyl group is at a higher chemical shift than the proton in cyclohexene 6 05 ppm for cyclohexenone vs.

The o h and n h protons are exchangeable and this is handy feature because when in doubt you can add a drop of deuterated water d 2 o and make the signal disappear since deuterium does not resonate in the region where protons do. For vinylic protons in a trans configuration we see coupling constants in the range of 3j 11 18 hz while cis protons couple in the 3j 5 10 hz range. Other groups that give broad and sometimes deuterium exchangeable signals are the amines amides and thiols. Typical proton proton coupling constants.

Proton b is bonded to a more electronegative atom s. The complementary process when a proton is added transferred to a brønsted lowry base is protonation or hydronation. Is this the proper resonance structure for the red proton s conjugate base. H2s also has a proton attached to an s and has a pka of 7 0 which is fairly acidic.

We know that a proton alpha to a carbonyl group is pulled downfield. The 2 bond coupling between protons on the same alkene carbon referred to as geminal protons is very fine generally 5 hz or lower. This is not surprising since the proton is not only vinylic but it is also alpha to a carbonyl group. Deprotonation or dehydronation is the removal transfer of a proton or hydron or hydrogen cation h from a brønsted lowry acid in an acid base reaction the species formed is the conjugate base of that acid.

Allyl is a name for this radical. The α protons of carbonyl groups are acidic because the negative charge in the enolate can be partially distributed in the oxygen atom. The species formed is the conjugate acid of that base.