[s30.93a]

Mc Lafferty can occur for C=O or C=C, thus yielding 105 and 121 as two peaks, but which one will be base peak?

[MOTOBALL]

The base peak is that with the greatest relative intensity, so what determines rel int. Once an ion has been formed?

[s30.93a]

Obviously, the most stable cation will resemble base peak, if C=O will break its α-β bond -C-O⁺H will form, in other case -C-C⁺H will be formed. Please correct me if I'm wrong and thus the latter is preferred

[MOTOBALL]

Ionization of R1-CO-R2 will give R1-CO+ and R2-CO+
Which in your case will be more stable ?

[s30.93a]

Ionization of R1-CO-R2 will give R1-CO+ and R2-CO+
Which in your case will be more stable ?

I think it depends on the stability of the radical R2° or R1° as R-CO⁺ is stabilised by back bonding. please correct if i'm worng
I made these structures depending on Mc Lafferty, please tell which one will be base peak?

[MOTOBALL]

Ionization of R1-CO-R2 will give R1-CO+ and R2-CO+
Which in your case will be more stable ?

[MOTOBALL]

I don't believe that your drawn structure is 1-phenyl-1-butanone.
Please check !

[AWK]

Search NIST for MS of butyrophenon

[MOTOBALL]

Search NIST for MS of butyrophenon

AWK,
Why provide the answer on a platter, when our job is to help them think it through for themselves?

[AWK]

s30.93a discusses other compound (2-propyl-3,4-dihydro-2H-naphthalen-1-one). Two main peaks of butyrophenon are 105 and 77. Title of thread is incorrect.

[s30.93a]

No, i want to know base peak for both the compounds.
The latter which I posted has more possibilities for Mc Lafferty.
I want to know which of the fragmentation is preferred, thus I'll subsequently apply that fact to 1-phenyl-1-butanone

[s30.93a]

Search NIST for MS of butyrophenon

AWK,
Why provide the answer on a platter, when our job is to help them think it through for themselves?

I already knew such databases, but looking for reasons.

[AWK]

Then start from easier compound - butyrophenone. Show us McLafferty rearrangement
and two α-cleavages for this compound.

[s30.93a]

Then start from easier compound - butyrophenone. Show us McLafferty rearrangement
and two α-cleavages for this compound.

These are the two possible rearrangements.

[AWK]

These not give ions 105 and 77 which are most abundant in the spectrum of butyrophenone. Check α-cleavages.