1H NMR study of the hetero-association of unsaturated alcohols with pyridine

作者：Lomas John S^*

来源：Journal of Physical Organic Chemistry, 2012, 25(8): 620-627.

DOI：10.1002/poc.1953

• alkenols
• alkynols
• hydrogen bonding
• OH shifts
• Taft polar constants

The 1H NMR titration method is used to investigate the association of some unsaturated alcohols with pyridine in benzene. The association constant for allyl alcohol (2-propen-1-ol) is slightly higher than for alkanols, but putting one methylene group between the OH and vinyl group completely eliminates this enhancement. In alkynols both the OH and?=CH protons associate with pyridine. Here, the effects of chain-lengthening on the association constant are irregular. Values for alkynols and some alcohols with hetero-atom substituents are lower than expected on the basis of a Taft polar constant (s*) correlation of alkanol association constants and of a correlation with the pKas of the corresponding carboxylic acids. It is suggested that stabilization of the ground state by OH/p interactions is responsible for these low association constants. Small increases in the NMR shifts of the OH protons in the 3-carbon and 4-carbon alkenols and alkynols can also be attributed to OH/p interactions, but the 5-carbon analogues have shifts as low as alkanols.

• 出版日期2012-8