Question

Minoxidil \(\left(\mathrm{C}_{9} \mathrm{H}_{15} \mathrm{~N}_{5} \mathrm{O}\right)\) is a compound produced by Pharmacia Company that has been approved as a treatment of some types of male pattern baldness. a. Would minoxidil be more soluble in acidic or basic aqueous solution? Explain. b. Give the hybridization of the five nitrogen atoms in minoxidil. c. Give the hybridization of each of the nine carbon atoms in minoxidil. d. Give approximate values of the bond angles marked \(a, b, c\), \(d\), and \(e .\) e. Including all the hydrogen atoms, how many \(\sigma\) bonds exist in minoxidil? f. How many \(\pi\) bonds exist in minoxidil?

Short answer

a. Minoxidil would be more soluble in acidic aqueous solution due to the presence of nitrogen atoms that can be protonated in acidic conditions. b. All five nitrogen atoms in Minoxidil have sp2 hybridization. c. The hybridization of the nine carbon atoms in Minoxidil are: sp, sp2, sp3, sp3, sp3, sp3, sp3, sp3, sp3. d. The approximate values of the bond angles \(a, b, c, d\), and \(e\) in Minoxidil are: 120°, 120°, 120°, 120°, and 109.5°, respectively. e. Including all the hydrogen atoms, there are a total of 22 σ bonds in Minoxidil (twenty-one from single bonds and one from the double bond). f. There is one π bond in Minoxidil, which is part of the double bond between the two nitrogen atoms.

Step-by-step solution

Draw the Lewis structure

Let's start by drawing the Lewis structure of Minoxidil. We can do this by joining the carbon, nitrogen, hydrogen, and oxygen atoms according to the given formula, and arranging the lone pairs of electrons so that the octet rule is satisfied for each atom. Here is the Lewis structure of Minoxidil: ``` N---N // \ N C---C---C---C---O || || | | N---C---N H H \ H ```

Determine the solubility

To determine whether Minoxidil would be more soluble in acidic or basic aqueous solution, we need to identify the functional groups in the molecule and check if they can be protonated (in acidic solution) or deprotonated (in basic solution). In Minoxidil, we can see that there are nitrogen atoms present in the structure. Nitrogen can be protonated under acidic conditions, forming a positively charged ammonium group. Since "like dissolves like," Minoxidil will be more soluble in an acidic aqueous solution because of its ability to form interactions with the polar water molecules. #a.# Minoxidil would be more soluble in acidic aqueous solution due to the presence of nitrogen atoms that can be protonated in acidic conditions.

Determine the hybridization of nitrogen atoms

The hybridization of the five nitrogen atoms in Minoxidil can be determined by checking the electron domains around each nitrogen atom. 1. The nitrogen atom at the top left has two bonded atoms and one lone pair. Since it's involved in three electron domains, it has sp2 hybridization. 2. The nitrogen atom at the top has one bonded atom and two lone pairs. Since it's involved in three electron domains, it has sp2 hybridization. 3. The nitrogen atom in the middle left has three bonded atoms and no lone pairs. Since it's involved in three electron domains, it has sp2 hybridization. 4. The nitrogen atom at the bottom left has two bonded atoms and one lone pair. Since it's involved in three electron domains, it has sp2 hybridization. 5. The nitrogen atom in the middle has two bonded atoms and one lone pair. Since it's involved in three electron domains, it has sp2 hybridization. #b.# All five nitrogen atoms in Minoxidil have sp2 hybridization.

Determine the hybridization of carbon atoms

To determine the hybridization of the nine carbon atoms in Minoxidil, let's check the electron domains around each carbon atom. 1. The carbon atom at the top right has two bonded atoms and no lone pairs. Since it's involved in two electron domains, it has sp hybridization. 2. The carbon atom below the top right has three bonded atoms and no lone pairs. Since it's involved in three electron domains, it has sp2 hybridization. 3. The carbon atom in the middle right has four bonded atoms and no lone pairs. Since it's involved in four electron domains, it has sp3 hybridization. 4. The carbon atom at the bottom right has four bonded atoms and no lone pairs. Since it's involved in four electron domains, it has sp3 hybridization. 5-9. All other carbon atoms have four bonded atoms and no lone pairs. Since they are involved in four electron domains, they all have sp3 hybridization. #c.# The hybridization of the nine carbon atoms in Minoxidil are: sp, sp2, sp3, sp3, sp3, sp3, sp3, sp3, sp3.

Determine bond angles

Let's determine the approximate values of the bond angles marked \(a, b, c, d\), and \(e\) in the Minoxidil molecule: 1. Angle \(a\) is between two nitrogen atoms and a carbon atom, all with sp2 hybridization. The bond angle for an sp2 hybridized atom is approximately 120°. Therefore, angle \(a\) ≈ 120°. 2. Angle \(b\) is between two nitrogen atoms and a carbon atom, all with sp2 hybridization. The bond angle for an sp2 hybridized atom is approximately 120°. Therefore, angle \(b\) ≈ 120°. 3. Angle \(c\) is between two carbon atoms and a nitrogen atom, all with sp2 hybridization. The bond angle for an sp2 hybridized atom is approximately 120°. Therefore, angle \(c\) ≈ 120°. 4. Angle \(d\) is between two carbon atoms and an oxygen atom, with the carbon atom having sp2 hybridization, and oxygen having sp3 hybridization. The bond angle for an sp2 hybridized atom is approximately 120°. Therefore, angle \(d\) ≈ 120°. 5. Angle \(e\) is between an sp3 hybridized carbon atom, a nitrogen atom with sp2 hybridization, and a hydrogen atom. The bond angle for an sp3 hybridized atom is approximately 109.5°. Therefore, angle \(e\) ≈ 109.5°. #d.# The approximate values of the bond angles \(a, b, c, d\), and \(e\) in Minoxidil are: 120°, 120°, 120°, 120°, and 109.5°, respectively.

Determine the number of σ and π bonds

To determine the number of σ and π bonds in Minoxidil, we need to count the single, double, and triple bonds in the Lewis structure: 1. There are a total of 21 single bonds in the Minoxidil molecule, including twelve C-H, five C-N, two N-N, one C-C, and one C-O bond. All single bonds are σ bonds. 2. There is one double bond between two nitrogen atoms in the Minoxidil molecule. A double bond consists of one σ bond and one π bond. #e.# Including all the hydrogen atoms, there are a total of 22 σ bonds in Minoxidil (twenty-one from single bonds and one from the double bond). #f.# There is one π bond in Minoxidil, which is part of the double bond between the two nitrogen atoms.

Key concepts

Acidic Solubility

Minoxidil's solubility in acidic versus basic conditions is a key aspect of its chemical behavior. When a compound like Minoxidil contains nitrogen atoms, an interesting interaction occurs in acidic solutions. Here’s why: in the presence of an acid, these nitrogen atoms can accept a hydrogen ion (a proton), forming a positively charged ammonium ion.

This process, known as protonation, enhances Minoxidil's solubility in acidic aqueous solutions. The protonated nitrogen atoms engage more effectively with water molecules due to their charge, thus improving solubility.

1. **Functional Group Presence**: Nitrogen atoms make this possible. 2. **Protonation**: Forms ammonium ions in acidic solutions. 3. **Polar Interaction**: Enhances water solubility due to ionic attraction. Essentially, Minoxidil's structural features make it more soluble under acidic conditions, facilitating better interactions with the solvent, water.

Nitrogen Hybridization

In molecular geometry, hybridization helps explain the shape and bond angles of molecules. Minoxidil features five nitrogen atoms, each with its specific hybridization state, influencing the molecule's structure.

All five nitrogen atoms in Minoxidil are sp2 hybridized, meaning each nitrogen forms three sigma (\(\sigma\)) bonds and has one lone pair of electrons. This configuration typically results from having three electron domains. Notably, sp2 hybridization is important for molecules with double bonds or lone pairs.

- **Electron Domains**: There are three around each nitrogen.- **sp2 Hybridization**: Forms one \(\pi\) bond, often seen in aromatic compounds.The sp2 hybridization of nitrogen in Minoxidil contributes to the planarity and rigidity of the structure, essential for its chemical properties and interactions.

Carbon Hybridization

Carbon atoms play a vital role in the structure of organic compounds like Minoxidil, where they exhibit different hybridizations. Each type of hybridization corresponds to a specific bonding arrangement:

- **sp Hybridization**: Found when carbon is bonded to two atoms, forming a linear geometry with a bond angle of 180°. - **sp2 Hybridization**: Occurs when carbon is bonded to three atoms, forming a trigonal planar shape with angles about 120°. - **sp3 Hybridization**: Occurs when carbon forms four bonds, leading to a tetrahedral shape with bond angles of approximately 109.5°. In Minoxidil: - One carbon is sp hybridized. - One carbon is sp2 hybridized. - The remaining carbons are sp3 hybridized. This diverse hybridization allows for a complex molecule with varied bond angles and strengths.

Bond Angles

Understanding bond angles in molecules like Minoxidil helps predict the shape and spatial arrangement, which is critical for understanding molecular interactions.

1. **Angle a, b, c, d**: These involve atoms with sp2 hybridization, so they are close to 120°. These angles reflect a trigonal planar geometry commonly seen in molecules with sp2 hybridized atoms. 2. **Angle e**: This involves sp3 hybridization, leading to a bond angle of approximately 109.5°, characteristic of tetrahedral geometry. These specific geometries and angles create a three-dimensional structure that supports Minoxidil's biological activity. Such angles allow for interactions with biological targets, underlying its therapeutic uses.

Sigma and Pi Bonds

Bonds in Minoxidil include both sigma (\(\sigma\)) and pi (\(\pi\)) bonds, each with unique roles. Sigma bonds are single bonds vital for structural integrity, whereas pi bonds form part of double bonds.

- **Sigma (\(\sigma\)) Bonds**: In Minoxidil, all single bonds are sigma bonds. There are a total of 22 sigma bonds, including carbon-hydrogen, carbon-carbon, carbon-nitrogen, nitrogen-nitrogen, and carbon-oxygen bonds.

- **Pi (\(\pi\)) Bonds**: These result from the overlap of unhybridized p orbitals above and below the sigma bond axis. Minoxidil contains one pi bond, contributing to the rigidity and planarity of the molecule.Together, these bonds maintain Minoxidil's shape and influence its chemical reactivity and solubility, critical factors in its effectiveness as a treatment for baldness.