Passage
Amino acids and copper both serve vital roles in many biological processes of living organisms. Beyond their separate biological roles, however, chemists have also discovered that amino acids are able to function as chelates with Cu²⁺ ions to form blue complexes with potential medicinal applications. One such complex, copper(II) glycinate, has shown to be effective against some oral diseases. The reaction to form copper(II) glycinate is shown in Figure 1.
Figure 1 Synthesis of two isomers of copper(II) glycinateTwo different isomers can form depending on the reaction conditions. Mixing hot aqueous glycine (70 °C) with a hot solution of copper(II) acetate dissolved in 50% aqueous ethanol, followed by cooling the mixture on ice, yields a precipitate of only the cis isomer. If a suspension of the cis isomer is held at boiling for an hour or longer in a solution of glycine and copper(II) acetate, the trans isomer is obtained.Because of the geometric differences between the two isomers, the stretching vibrations of the central Cu-N and Cu-O bonds in each isomer are different. Symmetric and asymmetric bond stretching give four possible vibrational modes for each isomer, as shown in Figure 2.
Figure 2 Vibrational modes of the coordinate bonds in copper(II) glycinateIf the stretching of the bonds during vibration causes a transient, unequal distribution of electron density between the atoms within the bond, an oscillating dipole will form. Bonds with dipoles that are not cancelled out by another dipole in the molecule will absorb infrared light at particular frequencies (often expressed in wave numbers) and are designated as IR-active. As a result, the vibrational differences between the two isomers can be analyzed by far-infrared (far-IR) spectroscopy, as shown in Figure 3.
Figure 3 Far-IR spectra of the cis and trans isomers of copper(II) glycinateBoth isomers show a skeletal absorbance (unrelated to coordinate bond vibration) near 385 cm⁻¹. Additional absorbance bands are seen that specifically relate to the vibrational modes of the bonds in each isomer.
-The copper(II) glycinate isomers contain atoms with different hybridization states. Based on the chemical structure shown above, which of the indicated atoms in the trans isomer are NOT sp³ hybridized? (Note: Ignore any effects from resonance contributors.)

Question

Passage
Amino acids and copper both serve vital roles in many biological processes of living organisms. Beyond their separate biological roles, however, chemists have also discovered that amino acids are able to function as chelates with Cu²⁺ ions to form blue complexes with potential medicinal applications. One such complex, copper(II) glycinate, has shown to be effective against some oral diseases. The reaction to form copper(II) glycinate is shown in Figure 1.

Figure 1 Synthesis of two isomers of copper(II) glycinateTwo different isomers can form depending on the reaction conditions. Mixing hot aqueous glycine (70 °C) with a hot solution of copper(II) acetate dissolved in 50% aqueous ethanol, followed by cooling the mixture on ice, yields a precipitate of only the cis isomer. If a suspension of the cis isomer is held at boiling for an hour or longer in a solution of glycine and copper(II) acetate, the trans isomer is obtained.Because of the geometric differences between the two isomers, the stretching vibrations of the central Cu-N and Cu-O bonds in each isomer are different. Symmetric and asymmetric bond stretching give four possible vibrational modes for each isomer, as shown in Figure 2.

Figure 2 Vibrational modes of the coordinate bonds in copper(II) glycinateIf the stretching of the bonds during vibration causes a transient, unequal distribution of electron density between the atoms within the bond, an oscillating dipole will form. Bonds with dipoles that are not cancelled out by another dipole in the molecule will absorb infrared light at particular frequencies (often expressed in wave numbers) and are designated as IR-active. As a result, the vibrational differences between the two isomers can be analyzed by far-infrared (far-IR) spectroscopy, as shown in Figure 3.

Figure 3 Far-IR spectra of the cis and trans isomers of copper(II) glycinateBoth isomers show a skeletal absorbance (unrelated to coordinate bond vibration) near 385 cm⁻¹. Additional absorbance bands are seen that specifically relate to the vibrational modes of the bonds in each isomer.
-The copper(II) glycinate isomers contain atoms with different hybridization states.

Based on the chemical structure shown above, which of the indicated atoms in the trans isomer are NOT sp³ hybridized? (Note: Ignore any effects from resonance contributors.)

Quizplus · Accepted Answer

11ecba2d_120d_9fd5_a3bf_b37cc0a1757d_MD0008_00 Hybridization is the process by which two or more atomic orbitals combine to form new hybrid orbitals that have different shapes and spatial orientations than the atomic orbitals that produce them. Different types of hybrid orbitals (hybrid states) are produced depending on the number and type of orbitals that combine. For example, if an s atomic orbital combines with three p atomic orbitals (four atomic orbitals total), conservation of orbitals requires that four hybrid orbitals are produced; therefore, four equivalent sp³ hybrid orbitals result. However, combining only two p atomic orbitals with an s atomic orbital (three total) produces three sp² hybrid orbitals (a different kind of hybrid orbital). The spatial orientations adopted by hybrid orbitals to minimize electronic repulsion depend on the number of hybrid orbitals formed. Determining hybridization only requires an examination of the number of unique orbital vectors (directions) occupied by bonds and/or lone pair electrons around each atom. In trans-copper(II) glycinate, both atoms in the C=O bond have three vectors. Carbon has one vector from each single bond and one vector from the double bond. Likewise, oxygen has one vector from the double bond, but it has two vectors from the lone pairs of electrons. Therefore, the C and O atoms in the C=O bond are not sp³ hybridized because sp³ hybridization orients in four vectors. (Choices B, C, and D) The O and N atoms bonded to Cu are both sp³ hybridized. The N atom has four vectors (one from each of its four bonds), and the O atom has two vectors from the two bonds and two vectors from the two lone pairs of electrons (four vectors total). Although the O atoms may participate in resonance, the question states to ignore any effects from resonance and evaluate the configuration of the structure as shown. Educational objective: During hybridization, atomic orbitals combine to form new hybrid orbitals that assume spatial orientations to minimize the electronic repulsion between orbitals. The number of hybrid orbitals that form and the number of orientational vectors adopted by the hybrid orbitals will equal the number of atomic orbitals that combine.

Passage Amino Acids and Copper Both Serve Vital Roles in Many