CHEM 2443 Chapter Notes - Chapter 10: Nitric Acid, Nucleophile, Counterion

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Avery welch organic chemistry chapter 10: reactions of alkenes & alkynes weeks 10-11: a carbocation with 3 attached carbon groups is a tertiary carbocation. R3c: a secondary carbocation has 2 attached carbon groups. R2hc: a primary carbocation has one attached carbon group. Rh2c: a methyl carbocation has no attached carbon groups. H3c: a tertiary carbocation is more stable than a secondary, secondary is more stable than primary, primary is more stable than methyl. From this analysis, a generalized assumption can be made that when an alkene reacts with an acid hx, the reaction will generate the more stable carbocation intermediate. The overall structure has a formal charge of +1, but that charge resides on the sp2- hybridized carbon atom. The positive charge on carbon leads to an induced dipole on the adjacent atoms, so if there are carbon groups attached to c+, each attached carbon will be negatively charged.

Related Questions

A. How could their mass spectra be used to distinguish between the following compounds?

3-methyl-2-butanone, 3-pentanone, 2-pentanone

3-Methyl-2-butanone will have a peak at m/z=58 due to a McLafferty rearrangement.

3-Pentanone will have a peak at m/z=58 due to a McLafferty rearrangement.

3-Methyl-2-butanone will have a base peak at m/z=57, whereas the other two ketones will have base peaks at m/z=43.

2-Pentanone will have a peak at m/z=58 due to a McLafferty rearrangement.

3-Methyl-2-butanone does not have any ?-hydrogens. Therefore, it cannot undergo a McLafferty rearrangement, so it will not have a peak at m/z=58.

3-Pentanone will have a base peak at m/z=57, whereas the other two ketones will have base peaks at m/z=43.

3-Pentanone has ?-hydrogens. Therefore, it cannot undergo a McLafferty rearrangement, so it will not have a peak at m/z=58.

2-Pentanone will have a base peak at m/z=57, whereas the other two ketones will have base peaks at m/z=43.

B. What would distinguish the mass spectrum of 2,2-dimethylpropane from the mass spectra of pentane and 2-methylbutane?

	The peak at m/z=57 is due to loss of a methyl radical: loss of a methyl radical from 2,2-dimethylpropane forms a tertiary carbocation, whereas loss of a methyl radical from 2-methylbutane forms a less stable secondary carbocation.
	The peak at m/z=57 will be more intense for 2,2-dimethylpropane than for 2-methylbutane or pentane.
	The peak at m/z=57 is due to loss of a methyl radical: loss of a methyl radical from 2,2-dimethylpropane forms a tertiary carbocation, whereas loss of a methyl radical from 2-methylbutane forms a more stable secondary carbocation.
	The peak at m/z=43 will be most intense for 2-methylbutane because such a peak is due to loss of an ethyl radical, which forms a secondary carbocation.
	The peak at m/z=57 is due to loss of a methyl radical: loss of a methyl radical from 2,2-dimethylpropane forms a secondary carbocation, whereas loss of a methyl radical from pentane forms a more stable primary carbocation.
	The peak at m/z=57 will be more intense for pentane than for 2-methylbutane or 2,2-dimethylpropane.
	The peak at m/z=57 is due to loss of a methyl radical: loss of a methyl radical from 2,2-dimethylpropane forms a tertiary carbocation, whereas loss of a methyl radical from pentane forms a less stable primary carbocation.
	The peak at m/z=43 will be most intense for 2,2-dimethylpropane because such a peak is due to loss of an ethyl radical, which forms a secondary carbocation.

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CHEM 2443 Chapter Notes - Chapter 10: Nitric Acid, Nucleophile, Counterion

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