Amides: Structure, Stability, and Properties

Professor Dave discusses amides, focusing on their structure, properties, and significance in both organic chemistry and biochemistry. He explains the unique characteristics of amides, such as the energy barrier for rotation around the C-N bond and their resonance structures. The video also covers dimethyl formamide (DMF) as a common solvent, the isomerism in secondary amides, and the critical role of amides in protein structure and stability. The discussion concludes with a brief mention of future topics in protein synthesis.

What is the structural feature that defines an amide?

• A nitrogen atom bonded to three hydrogen atoms

• A carbonyl group adjacent to an oxygen atom

• A carbonyl group adjacent to a nitrogen atom

• A carbonyl group adjacent to a sulfur atom

Why is the rotation around the C-N bond in amides restricted?

• Because the nitrogen atom is sp3 hybridized

• Because of the zwitterionic resonance structure

• Due to the presence of a triple bond

• Due to steric hindrance from large groups

What does the IR spectroscopy data indicate about the carbonyl stretch in DMF?

• It cannot be detected in IR spectroscopy

• It shows a lower wavenumber than ketones

• It shows a higher wavenumber than ketones

• It is identical to the wavenumber of ketones

In a typical NMR spectrum of DMF, what happens to the methyl signals as the temperature increases?

• They remain as two distinct signals

• They disappear completely

• They broaden and coalesce into a singlet

• They split into multiple peaks

What is the main reason for the stability of the trans isomer in secondary amides?

• It has a lower energy barrier for rotation

• It forms stronger hydrogen bonds

• It is more stable due to steric factors

• It has a higher energy barrier for rotation

What percentage of amino acid residues in proteins contain cis peptide bonds?

• Approximately 10%

• About 50%

• Less than 0.1%

• More than 90%

Why are amides not easily hydrolyzed in biological systems?

• Their stability is balanced to prevent easy hydrolysis

• They are protected by a protein shell

• They are surrounded by water which prevents hydrolysis

• They are too stable due to strong covalent bonds

What is the estimated half-life of a typical biological amide?

• Seven hours

• Seventy years

• Seven years

• Seven days

What would happen if amides were significantly more stable than they are?

• Proteins would hydrolyze too quickly

• Enzymes would struggle to promote hydrolysis

• Cells would easily obtain amino acids

• Proteins would not form at all

What is the significance of the particular stability of amides in proteins?

• It prevents proteins from forming

• It makes proteins indestructible

• It ensures proteins can be metabolized efficiently

• It allows proteins to dissolve in water