Question

Following are structural formulas for 1,4 -dioxane and piperidine. 1,4-Dioxane is a widely used solvent for organic compounds. Piperidine is found in small amounts in black pepper (Piper nigrum). C1CCNCC1 1,4-Dioxane Piperidine (a) Complete the Lewis structure of each compound by showing all unshared electron pairs. (b) Predict bond angles about each carbon, oxygen, and nitrogen atom. (c) Describe the most stable conformation of each ring and compare these conformations with the chair conformation of cyclohexane.

Short answer

Question: Draw the complete Lewis structure for 1,4-dioxane and piperidine and predict bond angles around each carbon, oxygen, and nitrogen atom. Describe the most stable conformation of each ring and compare these conformations with the chair conformation of cyclohexane. Answer: In 1,4-dioxane, each oxygen atom has two lone pairs, and bond angles around carbon atoms are approximately 109.5°, while bond angles involving oxygen atoms are approximately 104.5°. In piperidine, the nitrogen atom has one lone pair, and bond angles around carbon atoms are approximately 109.5°, while the bond angle between the connected carbon atoms and nitrogen is around 107°. The most stable conformation of 1,4-dioxane is the chair conformation, whereas the most stable conformation of piperidine is a boat conformation.

Step-by-step solution

Draw the complete Lewis structure for each compound

First, let's draw the complete Lewis structure for 1,4-dioxane and piperidine by adding unshared electron pairs. 1,4-Dioxane: Oxygen atoms have 6 valence electrons and need 2 more to complete their octet. So, each oxygen atom should have two lone pairs (unshared electrons). Piperidine: Nitrogen atom has 5 valence electrons and needs 1 more to complete its octet. Thus, it should have one lone pair (unshared electrons). Once you place the lone pairs on the structures, the complete Lewis structures are obtained.

Predict bond angles around each atom

Let's predict the bond angles around each carbon, oxygen, and nitrogen atom in both compounds. 1,4-Dioxane: Carbon atoms have tetrahedral electron pair geometry, and each bond angle around carbon atoms is approximately 109.5°. Oxygen atoms have a bent molecular geometry with two lone pairs, and each bond angle involving the oxygen atom is approximately 104.5°. Piperidine: Carbon atoms have tetrahedral electron pair geometry, and each bond angle around carbon atoms is approximately 109.5°. Nitrogen atom has trigonal pyramidal electron pair geometry with one lone pair, so the bond angle between the connected carbon atoms and nitrogen is around 107°.

Describe the most stable conformation and compare with cyclohexane

Let's describe the most stable conformation of each ring and compare these conformations with the chair conformation of cyclohexane. 1,4-Dioxane: The most stable conformation of 1,4-dioxane is called the "chair" conformation, just like cyclohexane, since it minimizes steric repulsions between the atoms in the ring. The oxygen atoms are "axial" in this conformation, which would be unfavorable for substituents with larger groups. However, for 1,4-dioxane, the chair conformation is still the most stable state. Piperidine: The most stable conformation of piperidine is a "boat" conformation, where the nitrogen atom is in an equatorial position and the other carbon atoms are in a chair-like structure. The boat conformation minimizes the steric repulsion between the hydrogen atoms bonded to nitrogen and the other carbon atoms in the ring. This conformation is different from the chair conformation of cyclohexane, wherein all carbon atoms are in the same plane.

Key concepts

Lewis Structures

Understanding the Lewis structure of a molecule is a fundamental skill in organic chemistry. It is a pictorial representation of the arrangement of valence electrons around atoms within a molecule. The Lewis structure helps us understand the types of bonds present (single, double, triple), the number of lone pairs on each atom, and the overall molecular geometry.

For 1,4-dioxane and piperidine, the complete Lewis structures indicate not only the shared electron pairs that constitute bonds between atoms but also the unshared (lone) pairs of electrons that are crucial for both the stability and reactivity of these molecules. In 1,4-dioxane, two oxygen atoms each have two lone pairs, while in piperidine, the nitrogen atom has one lone pair. Correctly drawing Lewis structures leads to better prediction of reaction mechanisms and the behavior of molecules in various chemical processes.

Bond Angles Prediction

Predicting bond angles is essential in understanding the three-dimensional shape of molecules. The bond angles are influenced by the molecule's electron pair geometry, which is dictated by the VSEPR (Valence Shell Electron Pair Repulsion) theory. It states that electron pairs around a central atom arrange themselves to minimize repulsion.

When analyzing 1,4-dioxane, with its tetrahedral carbon atoms, one can expect bond angles close to 109.5°. The oxygen atoms, however, will be slightly less due to the extra repulsion from the two lone pairs, typically around 104.5°. In piperidine, the carbon atoms also exhibit bond angles close to 109.5° due to their tetrahedral arrangement, but the bond angle around the nitrogen atom will be around 107° because of its trigonal pyramidal shape resulting from one lone pair. These predictions can guide us in visualizing the molecule's conformation and understanding its chemical behavior.

Conformational Analysis

Conformational analysis allows chemists to assess the different orientations that a molecule's atoms can assume due to rotation around single bonds. This is critical as it affects a molecule's physical and chemical properties. For cyclic compounds like 1,4-dioxane and piperidine, conformational analysis is particularly important because ring structures restrict the freedom of rotational movement.

The most stable conformation of 1,4-dioxane resembles the chair conformation seen in cyclohexane, which offers the least torsional strain and angle strain. For piperidine, however, the boat conformation is more favorable, avoiding the steric repulsion that would be observed if the nitrogen's lone pair was axial as in a chair conformation. Learning to visualize these conformations is crucial for understanding the stability and reactivity of cyclic organic molecules.

1,4-Dioxane Chemistry

1,4-Dioxane is a solvent with remarkable versatility in organic chemistry, particularly because of its ability to dissolve a wide range of chemical compounds. Its utility is also due to its conformational stability and relatively nonreactive ether linkages.

Understanding the chemistry of 1,4-dioxane involves recognizing its preference for a chair conformation with the oxygen atoms in axial positions. This knowledge has implications for its use as a solvent in various reactions, where it can host other organic molecules without imposing significant steric hindrance or electronic effects. On an industrial scale, 1,4-dioxane's solvent properties are employed in processes such as the manufacturing of pharmaceuticals and plastics.

Piperidine Chemistry

Piperidine, characterized by a six-membered ring containing one nitrogen atom, is an organic compound with significant presence in synthetic chemistry and natural products. The chemistry of piperidine is largely influenced by the basicity of the nitrogen atom, which impacts its reactivity in nucleophilic substitution and other reactions.

Its most stable conformation is indeed a boat, with nitrogen in an equatorial position that reduces steric hindrance. Piperidine's reactivity can be manipulated by adding various substituents to its ring, leading to a diverse array of derivatives important in synthesizing pharmaceuticals, agrochemicals, and other bioactive molecules. The study of piperidine and its derivatives is essential in the development of new compounds with medicinal properties.