Experiment 12: Electrophilic Aromatic Substitution - Acylation

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EAS FC Acylation

Due Dates:

5 Apr/6 Apr A/B

Chemical Safety Information:

Reagents, Some Potential Products, and Solvents (if available)
iron (III) chloride propionyl chloride anisole
dichloromethane deuterated chloroform magnesium sulfate
2′-Methoxypropiophenone 3′-Methoxypropiophenone 4′-Methoxypropiophenone

 

Experimental Spectra:

EAS Nitration 1H-NMR 17-Jul-2015
EAS Nitration 1H-NMR 17-Jul-2015

Sample 1H-NMR Acylation Starting Material (not available for submission for credit)

Sample 1H-NMR Acylation Product (not available for submission for credit)

Stock 1H-NMR FID Acylation Product (available for submission for credit, see laboratory manual for details)

Stock IR Acylation Product Stock Spectrum (available for submission for credit, see laboratory manual for details)

Stock GC-MS EAS FC Acylation Product (available for submission for credit, see laboratory manual for details)

 

Frequently Asked Questions:

Q1) Why are the structures drawn below not resonance structures of the same molecule?

badly drawn acylium resonance

A1)  This depiction of acylium resonance illustrates a fundamental misunderstanding about the definition and use of resonance structures.  Individual resonance structures, by definition, are not real represenations of the molecule.  A collection of two or more resonance structures taken together attempt to capture the bonding and electronic structure of the molecule.  In order for the resonance structures to meaningfully sum to a reasonable representation of the actual molecule, the geometry cannot change from one structure to another.  Specific to the case above, the oxygen atom moves location from one structure to another; this IS NOT allowed.  Acyllium ions are not bent as depicted for the left structure; the structure on the right is more meaningful.

 

Q2)  In what symmetry group should the acylium or propionylium cation be when correctly built or optimized?

A2)  Acylium and propionylium are linear along the C-C-O backbone.  Acylium has three H-atoms attached at the terminal C-atom, while propionylium has a methyl group substituted at that C-atom.  Acylium has a 3-fold axis of symmetry and its point group symmetry is C3V as shown below with symmetry elements displayed.  The methyl group in propionylium breaks up the 3-fold symmetry axis of acylium and reduces the symmetry to CS for propionylium.

Acylium C3V Acylium C3v
Acylium ion C3v (side view) Acylium ion C3v (end view)

 

Q3)  Does it matter whether I draw two bonds or three bonds between the carbon and oxygen atoms when making my input structure for the acylium electrophile?

A3)  All that matters is that your submitted input structure has atoms in about the correct locations and be of the correct symmetry.  It does not matter at all how many bonds WebMO thinks exists between any atoms.  The only required by Gaussian09 is the x,y,z coordinates of each atom; any bonds that are drawn are not used in the calculation.  In fact, both of the input structures below arrive at the same final geometry when optimized without any regard to the odd bonds drawn.  Notice that the atoms have not moved location and that the charge is +1 in both structures.

acylium acylium