Nitrogen and Phosphorus Containing Compounds Lecture
Key Topics Covered
Glycine's Chirality
Glycine does not have a chiral center because its α-carbon is not bonded to four different groups (H, H, NH2, COOH).
Glycine's structure excludes it from having enantiomers.
MCQ Insight: Glycine is the only amino acid without a chiral center among common amino acids, making it the correct answer for chirality questions (e.g., answer D for question 1).
Gabriel Synthesis Mechanism
Reactants: Methyl Bromide (electrophile) and thide (nucleophile).
Mechanism: Thide attacks methyl bromide, bromine leaves, resulting in methyl-thide.
Subsequent hydrolysis forms methyl amine.
MCQ Insight: Recognize the steps and resulting compounds that fit Gabriel synthesis (e.g., answer B for question 2).
Sulfur-Containing Amino Acids
Cysteine and Methionine contain sulfur.
Serine does not contain sulfur.
MCQ Insight: Familiarize yourself with structures to quickly identify sulfur containing amino acids (e.g., answer B for question 3).
Nylon Production and Amides
Amides form from an amine plus carboxyl group or its derivatives.
Hexane diamine and carboxylic acids likely initiate nylon production.
MCQ Insight: Substance X in nylon production is typically a carboxyl compound (e.g., answer B for question 4).
Strecker Synthesis Intermediates
Strecker synthesis intermediates include amine, imine, nitrile, but not amides.
MCQ Insight: Understand mechanisms and intermediates for this synthesis pathway (e.g., answer C for question 5).
Starting Materials for Strecker Synthesis
Starting material's carbonyl becomes the amino acid's alpha carbon and R group.
Proper starting reactant determines the resultant amino acid (e.g., valine needs two-methyl propanal; answer C for question 6).
Planar Geometry of CN Bond in Amides
One resonance structure shows double bond character between C and N.
Partial double bond character and SP2 hybridization contribute to planarity.
MCQ Insight: Recognize resonance and hybridization effects in amide bonds (e.g., answer D for question 7).
Optical Activity of Amino Acid Syntheses
Both Strecker and Gabriel syntheses produce racemic mixtures due to planar intermediates.
Racemic mixtures are optically inactive.
MCQ Insight: Neither synthesis results in optically active solutions (e.g., answer D for question 8).
Role of Thide in Gabriel Synthesis
Thide acts as a nucleophile attacking an electrophilic carbon.
MCQ Insight: Identify nucleophiles/electrophiles within synthesis mechanisms (e.g., answer A for question 9).
Reactions in Gabriel Synthesis
Includes nucleophilic substitution (SN2 reactions), hydrolysis, and decarboxylation, but not dehydration.
MCQ Insight: Know the sequence and type of reactions involved (e.g., answer C for question 10).
Phosphoric Acid Forms at Physiological pH
At pH 7, H2PO4- and HPO42- are the dominant forms due to proximity to pKa values.
MCQ Insight: Recognize pKa relationship to molecular forms (e.g., answer B for question 11).
Stability of Pyrophosphate
Pyrophosphate degrades into inorganic phosphate in aqueous solutions.
MCQ Insight: Expect breakdown into simpler phosphates (e.g., answer C for question 12).
Aspartic Acid's Charge at pH 7
Aspartic acid has two negative charges from carboxyl groups, balanced by one positive amino group.
Net charge: -1.
MCQ Insight: Calculate net charges considering ionizable groups (e.g., answer C for question 13).
Nucleotide Triphosphates in DNA Synthesis
When bonding, release occurs releasing pyrophosphate (PPi).
MCQ Insight: Understand byproduct release during bonding (e.g., answer A for question 14).
Buffering Capacity of Phosphoric Acid
Three hydrogens with pKa spread across wide pH range.
Allows moderate buffering capacity over large pH range (e.g., answer B for question 15).
Final Remarks
In summary, key takeaways include an understanding of synthesis reactions, molecular structures, and properties of amino acids and phosphates.
Familiarity with mechanisms and function groups aids in solving related MCQs effectively.