“GC-MSn analysis of the crude reaction mixtures from Friedel Craft acylation: unambiguous identification and differentiation of 3-aroylbenzofurans from their 4- and 6-regioisomers”

Begala et al. demonstrated isomeric differentiation of 3-, 4- and 6-aroylbenzofurans (2-phenylbenzofuran derivatives) by GC-MSn. In particular, they showed that OH radical loss was specifically observed in 2-nitrophenyl-benzofran derivatives and discussed its fragmentation pathway.

General comment
The manuscript is somewhat interesting though there are following concerns.

1. Reproducibility of MSn mass spectra were not evaluated. As mentioned in specific comments later, the MS3 mass spectra of 2a (Fig. 2F) should be identical to the MS3 mass spectra of 2b (Fig. 3F) because their precursor ions at m/z 298 have the same structure. However, there are differences between Fig. 2F and Fig. 3F (the ion at m/z 139 was observed in Fig. 2F but not in Fig. 3F). This result strongly suggests that reproducibility of the mass spectra should be checked. In addition, when isomers are differentiated by the relative intensity differences of the common product ion, an appropriate significant test such as Welch’s t-test is required to demonstrate their relative intensity differences.
2. The authors showed fragmentation pathways for 1c18O (Scheme 2), though reaction mechanisms of fragmentation pathways were not elucidated.

However, the manuscript demonstrated new findings for isomeric differentiation of 3-aroylbenzofrans, and thus, this manuscript has a potential for acceptance but major revision should be required.

Specific comments
P.6, line 40
The authors described “3-acyl isomer 1a together with traces of the 4-benzoyl isomer 2a and larger amount of the 6-benzoyl isomer 3a”, but the mass spectrometric sensitivity of each isomer is different from each other. Thus, quantitative description should be avoided here. Instead, the authors should describe “the ion intensity of each isomer is different from each other”.

P. 7 line 6 and Figure 2
1. Mass spectrum of 3a should be also shown in Figure 2.
2. Reproducibility of each ion in MS2 and MS3 mass spectra of 1a, 2a and 3a should be shown.

P. 7, line 15
The ion at m/z 221 was observed in mass spectrum of 1a. Thus, the description of “which is practically absent” is inappropriate. This description should be revised to “which is weak”.

P. 7, line 52 and Figure 3
1. Mass spectrum of 3b should be shown in Figure 3.
2. Reproducibility of each ion in MS2 and MS3 mass spectra of 1b, 2b and 3b should be shown.
3. The MS3 mass spectra of 1b (Fig. 3C) should be identical to the MS3 mass spectra of 1a (Fig. 2D) because their precursor ion at m/z 221 has a same structure. This is also the same for Fig. 3F (MS3 of 2b) and Fig. 2F (MS3 of 2a). However, there are differences between Fig. 2F and Fig. 3F (the ion at m/z 139 was observed in Fig. 2F but not in Fig. 3F). This result strongly suggests that reproducibility of the mass spectra should be checked. Thus, the authors should show reproducibility of MS2 and MS3 mass spectra for all targeted compounds.

P. 8, line 8
Practically absent -> weak

P. 8, line 38
thought -> through?

P. 8, lines 43-48
To prove isomeric differentiation by comparing the relative intensity of the common ion, an appropriate significant test such as Welch’s t-test should be performed. Thus, the authors should execute a significant test to prove the significant differences of the relative intensities at m/z 210 and 238 between 2c and 3c. Also, reproducibility of these ions should be shown.

P. 8, line 60-P. 9, line 8
This sentence is somewhat redundancy, and should be revised more concisely.

P. 9, line 48
Interesting ,-> interestingly,

Scheme 2
Here, the authors displayed fragmentation pathways for 1c18O (Scheme 2), though reaction mechanisms were not elucidated in detail. Thus, the authors should show reaction mechanisms for this fragmentation pathways in supplementary materials.