why is ammonia more acidic than an alkene?

[Bis-GMA111]

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if we were to compare NH3 vs. H-C=CH2 for instance...

we'd be comparing an sp3 ammonia vs. an sp2 alkene(which is more stable=weaker base=stronger acid?)

 

[flin5845]

if we were to compare NH3 vs. H-C=CH2 for instance...

we'd be comparing an sp3 ammonia vs. an sp2 alkene(which is more stable=weaker base=stronger acid?)

When comparing acid strengths use "CARDIO"
C-Charge (More negative stronger base=weaker acid)
A-Atom (More electronegative weaker base=stronger acid)
R-Resonance (More resonance=more stable base=stronger acid)
I-Induction (More electronegative atoms attached, better they withdraw=more stable base=Stronger acid)
O-orbital (sp>sp2>sp3..electrons closer to the nucleus=more stable=weaker base=stronger acid)


In your case, if we look at the Conjugate bases, -NH2 and -C=CH2.....Start with C...since both are negative then move to A, since N is more electronegative than Carbon, NH2- is the weaker base and therefore NH3 is the stronger acid...

Hope this helps..

EDIT: You may want to know the pKa: For Ammonia the pKa is about 33, an alkene pKa is about 44.

THE CARDIO WILL FAIL YOU WHEN COMPARING LIKE AMMONIA (PKA 33) TO A TERMINAL ALKYNE (PKA 26) BECAUSE AN SP LONE PAIR IS MORE STABLE THAN AN SP3 LONE PAIR.

 

[LetsGo2DSchool]

When comparing acid strengths use "CARDIO"
C-Charge (More negative stronger base=weaker acid)
A-Atom (More electronegative weaker base=stronger acid)
R-Resonance (More resonance=more stable base=stronger acid)
I-Induction (More electronegative atoms attached, better they withdraw=more stable base=Stronger acid)
O-orbital (sp>sp2>sp3..electrons closer to the nucleus=more stable=weaker base=stronger acid)


In your case, if we look at the Conjugate bases, -NH2 and -C=CH2.....Start with C...since both are negative then move to A, since N is more electronegative than Carbon, NH2- is the weaker base and therefore NH3 is the stronger acid...

Hope this helps..

EDIT: You may want to know the pKa: For Ammonia the pKa is about 33, an alkene pKa is about 44.

THE CARDIO WILL FAIL YOU WHEN COMPARING LIKE AMMONIA (PKA 33) TO A TERMINAL ALKYNE (PKA 26) BECAUSE AN SP LONE PAIR IS MORE STABLE THAN AN SP3 LONE PAIR.

Hey, what happened to the "D" in CARDIO? Is it just a filler letter?

 

[flin5845]

Hey, what happened to the "D" in CARDIO? Is it just a filler letter?

Haha didn't realize I skipped it. But it stands for dipole

C-charge
A-atom
R-resonance
D-dipole
I-induction
O-orbital