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Chapter 1: Problem 19

The following model is a representation of citric acid, a compound in the so- called citric acid cycle by which food molecules are metabolized in the body. Only the connections between atoms are shown; multiple bonds are not indicated. Complete the structure by indicating the positions of multiple bonds and lone-pair electrons (gray \(=\mathrm{C}, \mathrm{red}=\mathrm{O}\), ivory \(=\mathrm{H}\) ).

Short Answer

Expert verified
Citric acid has double bonds in carboxyl groups, and each oxygen in these receives two lone pairs.

Step by step solution

01

Identify Functional Groups

Citric acid is a tricarboxylic acid, meaning it has three carboxyl groups (-COOH). These groups will form the backbone of the molecule and are critical to determining the placement of multiple bonds and lone pairs.
02

Analyze Carboxyl Groups

The carboxyl group typically includes a carbon-oxygen double bond (C=O) and a hydroxyl (OH) group. For each carboxyl group, place a double bond between the carbon and one oxygen atom.
03

Add Hydrogen Atoms

For each of the carbon atoms, check the valency based on the typical tetra-valency rule which states that carbon can form four bonds. Add hydrogen atoms where necessary to satisfy this valency, ensuring all carbons make a total of four bonds.
04

Assign Lone Pairs on Oxygen

Oxygen atoms in the carboxyl group not forming a double bond will have lone pairs. Place two lone pairs on each singly-bonded oxygen (the oxygen in the OH group) to satisfy its stable electronic configuration.
05

Confirm Molecular Structure

Ensure that all atoms satisfy their usual oxidation states: carbon atoms should have four bonds, oxygen atoms should have two bonds and two lone pairs, and hydrogen atoms should have one bond. Double-check that the molecular structure reflects these oxidations accurately.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Citric Acid Cycle
The citric acid cycle, also known as the Krebs cycle or TCA cycle, is a central metabolic pathway that plays a critical role in energy production in cells. This cycle occurs within the mitochondria, which are often referred to as the powerhouses of the cell.

Here's how it works at a high level:
  • It takes place after glycolysis, the initial breakdown of glucose.
  • The cycle uses acetyl-CoA, a product derived from carbohydrates, fats, and proteins.
  • Through a series of enzymatic reactions, acetyl-CoA is oxidized, releasing energy stored in its chemical bonds.
  • This energy is captured in the form of ATP, the cell鈥檚 energy currency, along with electron carriers NADH and FADH鈧�.
The citric acid cycle is critical for cellular respiration because it provides the energy-rich molecules needed for the electron transport chain. The main products are:
  • ATP or GTP, which represents direct energy for cellular processes.
  • NADH and FADH鈧�, which are used in other cellular processes to generate more ATP.
  • Carbon dioxide, a waste product excreted by the cell.
Understanding this cycle is crucial because it highlights how food molecules are converted into usable energy, a process vital for sustaining life.
Tricarboxylic Acid
Tricarboxylic acids are organic acids containing three carboxyl groups. Citric acid is the namesake and prototype of this group, exemplifying how these acids behave and interact biochemically.

The remarkable characteristics of tricarboxylic acids include:
  • Their ability to form stable crystals due to multiple carboxyl groups, which facilitate hydrogen bonding.
  • High solubility in water, supported by the polar nature of carboxyl groups.
  • A sour taste, common to many carboxylic acids.
Citric acid, a tricarboxylic acid, plays an essential role both in the citric acid cycle and in various industries:
  • In the body, it participates in the storage, transport, and release of energy.
  • In food and beverage industries, it's used as a preservative and flavoring agent.
  • In cleaning products, citric acid serves as a natural cleanser due to its ability to bind with minerals.
Understanding tricarboxylic acids is crucial for grasping the broader context of biochemical functions and their practical applications.
Functional Groups
Functional groups are specific groupings of atoms that confer particular chemical properties to a molecule. They are the foundation of organic chemistry.

In the context of citric acid:
  • The most prominent functional group is the carboxyl group (-COOH).
  • This group influences the acidity and solubility of the molecule.
  • Due to the presence of carboxyl groups, citric acid can donate protons (H鈦�), making it an acid.
Within organic chemistry, functional groups determine the reactivity and interaction of a compound with other molecules. Some key characteristics include:
  • They allow prediction of the outcomes of chemical reactions.
  • Provide a way to classify compounds into families and predict related behaviors.
  • Are often the site of chemical reactions, preserving the backbone of the compound.
Understanding functional groups is vital for predicting and explaining how citric acid and similar compounds behave in both biological and industrial settings.

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Most popular questions from this chapter

Draw a line-bond structure for propane, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3} .\) Predict the value of each bond angle, and indicate the overall shape of the molecule.

Almost all stable organic species have tetravalent carbon atoms, but species with trivalent carbon atoms also exist. Carbocations are one such class of compounds. (a) How many valence electrons does the positively charged carbon atom have? (b) What hybridization do you expect this carbon atom to have? (c) What geometry is the carbocation likely to have?

Divalent carbon species called carbenes are capable of fleeting existence. For example, methylene, \(: \mathrm{CH}_{2}\), is the simplest carbene. The two unshared electrons in methylene can be either spin-paired in a single orbital or unpaired in different orbitals. Predict the type of hybridization you expect carbon to adopt in singlet (spin-paired) methylene and triplet (spinunpaired) methylene. Draw a picture of each, and identify the valence orbitals on carbon.

Draw a line-bond structure for propene, \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2} ;\) indicate the hybridization of each carbon; and predict the value of each bond angle.

Draw a line-bond structure for buta- 1,3 -diene, \(\mathrm{H}_{2} \mathrm{C}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}_{2} ;\) indicate the hybridization of each carbon; and predict the value of each bond angle.
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