Change to the methionine amino acid. How many valence electrons are in methionine? Table view List view 14b. Evaluating the methionine structure Measured bond angle VSEPR Idealized bond angle O=C-O C-S-C (S is yellow) H-N-C (H bound to N, N is blue) (1pts) 14c. Are these results for the methionine structure consistent with what you observed in Avogadro (within a few degrees)? Explain briefly.
The Correct Answer and Explanation is:
4a. Valence Electrons in Methionine
Methionine (C₅H₁₁NO₂S) is an amino acid, and the total number of valence electrons can be calculated by adding the valence electrons of each atom present in the molecule. Here’s the breakdown:
- Carbon (C): 4 valence electrons × 5 atoms = 20 electrons
- Hydrogen (H): 1 valence electron × 11 atoms = 11 electrons
- Nitrogen (N): 5 valence electrons × 1 atom = 5 electrons
- Oxygen (O): 6 valence electrons × 2 atoms = 12 electrons
- Sulfur (S): 6 valence electrons × 1 atom = 6 electrons
Total = 20 + 11 + 5 + 12 + 6 = 54 valence electrons
14b. Evaluating Methionine Structure
The structure of methionine involves several bonds. In particular, we are looking at the bond angles between atoms:
- O=C-O: This is a typical ester-like bond and will follow the ideal bond angle of 120° for the C=O bond (sp² hybridization).
- C-S-C (S is yellow): The sulfur atom has a single bond with carbon, so the bond angle around the carbon atoms would be close to 109.5°, typical for sp³ hybridized carbons in a tetrahedral arrangement.
- H-N-C (N is blue): The nitrogen here forms a single bond with carbon, with hydrogen bonded to nitrogen. Nitrogen usually follows an ideal bond angle of 107° due to its sp³ hybridization, which is slightly smaller than the typical 109.5° angle.
14c. Consistency with Avogadro Observations
In Avogadro, the molecular geometry of the methionine structure can be modeled and compared to idealized bond angles. Based on typical molecular geometry:
- The C=O bond should be close to 120° due to sp² hybridization, which aligns with the idealized bond angle in the table.
- The bond angles around the C-S-C and H-N-C groups would deviate slightly from ideal angles due to the nature of the bonds (lone pair electrons on nitrogen can slightly reduce the bond angle). However, the values should still fall within the expected range of 107°–109.5°.
These observed bond angles in Avogadro would likely be consistent with the idealized values but may vary slightly due to factors like lone pair repulsion or the exact geometry of the molecule. A difference of a few degrees is expected, especially in the case of nitrogen, where lone pairs influence the bond angle.
