Chemistry - Counting number of acidic-H in a molecule

An aldehyde or a ketone with an alpha hydrogen forms a carbanion that resonates to enolate form. This leads to two canonical structures that are in resonance. The example below is a polyphenol compound extracted from turmeric, called curcumin.

enter image description here

source: Biomaterials. 2010 May;31(14):4179-85. doi: 10.1016/j.biomaterials.2010.01.142. Epub 2010 Feb 23. (https://www.ncbi.nlm.nih.gov/pubmed/20181392)

The hydrogens between two keto groups are most acidic. This is due to formation of two equivalent enol structures stabilized by hydrogen bonding. The structural requirement would be planarity of atoms involved in hydrogen bonding.

Below are 3-D structures of the given compound in the question above.

  • Structure without hydrogens

Bridgehead carbon is 4. Keto groups are at 2 , 5 and 8 (shaded in grey). Keto groups on 5 and 8 are not in the same plane . Hence Hydrogen on 4 , 22 (see figure with hydrogens) does not form stable hydrogen bonded enol structures as discussed in the above example.

Therefore, hydrogen at 8th one (pointing with red arrow) may not be acidic.

Note: 3-D structures have been drawn on Chem3Dpro

enter image description here

  • Structure with hydrogens

enter image description here

  • Structure with hydrogens (2nd view)

enter image description here

Tags:

Related

Chemistry - Why isn't the American nickel magnetic? Chemistry - Writing half equation confusion Chemistry - How can we define a non-spontaneous reaction? Chemistry - When I burn isopropyl alcohol (IPA), it burns orange. But when I burn ethyl alcohol, it burns totally blue. Why is this? Chemistry - Are there ionic solids that conduct electricity? Chemistry - Understanding the use of Le Chatelier's principle in the industrial production of ammonia Chemistry - Generating electron density from protein coordinate (PDB) Chemistry - How can you build a model of tetrahedral coordination from objects found at home? Chemistry - What is the hidden meaning of electrochemical stability window? Chemistry - What does HClO2 aqueous solution decompose to in an open environment? Chemistry - Computing the commutator of the Fock and density matrices in AO basis (Hartree-Fock theory) Chemistry - What is the entropy of mixing a gas into the whole atmosphere?

Recent Posts