Problem 98 - Chemistry and Chemical Reactivity

Question

\- Acrylamide, \(\mathrm{H}_{2} \mathrm{C}=\mathrm{CHCONH}_{2},\) is a known neurotoxin and possible carcinogen. It was a shock to all consumers of potato chips and french fries a few years ago when it was found to occur in those products. (a) Sketch the molecular structure of acrylamide and identify all bond angles. (b) Indicate which carbon-carbon bond is the stronger of the two. (c) Is the molecule polar or nonpolar? (d) The amount of acrylamide found in potato chips is \(1.7 \mathrm{mg} / \mathrm{kg}\). If a serving of potato chips is \(28 \mathrm{g}\), how many moles of acrylamide are you consuming?

Step-by-Step Solution

Answer

Moles of acrylamide in 28 g of potato chips: \(6.70 \times 10^{-7}\). Stronger C-C bond: C=C. Acrylamide is polar.

Step 1: Sketching the molecular structure of acrylamide

Acrylamide, or \( \text{H}_2\text{C}=\text{CHCONH}_2 \), includes a double bond between two carbons (C=C), followed by a carbon that is double-bonded to an oxygen and single-bonded to a nitrogen (making a carbonyl group connected to an amide group). The entire structure is H2C=CH-C(=O)-NH2. The bond angles around the double-bonded carbons are approximately 120° due to sp2 hybridization, and around the nitrogen, they are approximately 120° as well, due to the planar geometry of the amide.

Step 2: Evaluating the strength of carbon-carbon bonds

The molecule has a C=C double bond and a C-C single bond. Double bonds are generally stronger than single bonds due to the presence of a pi bond in addition to the sigma bond. Thus, the C=C bond is the stronger of the two carbon-carbon bonds in acrylamide.

Step 3: Determining polarity of the molecule

Acrylamide has polar bonds due to differences in electronegativity, particularly around the carbonyl group (C=O). The presence of polar groups and the asymmetric shape of the molecule means that acrylamide is likely a polar molecule.

Step 4: Calculating moles of acrylamide in a serving of potato chips

First, find the mass of acrylamide in 28 g of potato chips. Using a concentration of 1.7 mg/kg, convert the serving to kilograms: \( 28 \text{ g} = 0.028 \text{ kg} \). Calculate the mass of acrylamide as: \( 1.7 \text{ mg/kg} \times 0.028 \text{ kg} = 0.0476 \text{ mg} \). Convert this mass to grams: \( 0.0476 \text{ mg} = 0.0000476 \text{ g} \). The molar mass of acrylamide is \( 71.08 \text{ g/mol} \) (C3H5NO). Finally, find the moles of acrylamide by dividing the mass by the molar mass: \( \frac{0.0000476 \text{ g}}{71.08 \text{ g/mol}} = 6.70 \times 10^{-7} \text{ moles} \).

Key Concepts

Neurotoxin

A neurotoxin is a type of chemical substance that adversely affects the nervous system. These compounds can interfere with neuron communication by disrupting nerve signals. Acrylamide is categorized as a neurotoxin because it impacts the central and peripheral nervous systems. Although frequently debated for its potential health hazards, like being a suspected carcinogen, acrylamide has been found in common foods such as potato chips and french fries. This naturally raises concerns about our daily exposure to such substances.
Understanding neurotoxins is crucial because:

• They can cause symptoms ranging from mild headaches to severe neurological damage.
• Chronic exposure might increase the risk of developing neurodegenerative diseases.
• Recognizing them allows for the implementation of safety measures to reduce potential risks.

Monitoring your exposure to neurotoxins can help maintain a healthy nervous system and overall better well-being.

Molecular structure

The molecular structure of a compound, like acrylamide, tells us how its atoms are arranged in space. Acrylamide consists of a carbon backbone with functional groups attached — specifically, an amide group and a carbonyl group. In acrylamide’s structure, each type of atom contributes to the molecule's shape and properties. Considering its formula, \( ext{H}_2 ext{C}= ext{CHCONH}_2 \), the molecule appears with specific angles due to hybridization.
Key aspects of acrylamide's molecular structure include:

• Double bonds: The carbon-carbon double bond (C=C) creates rigidity and planar geometry around itself.
• Functional groups: The amide and carbonyl groups are critical for determining reactivity and interactions.
• Bond angles: Approximately 120°, around the double-bonded carbons, due to sp2 hybridization — leading to a flat, trigonal planar shape.

This structure's simplicity belies the complexity of its interactions, particularly in biological systems.

Chemical polarity

Polarity in molecules, like acrylamide, is determined by the unequal sharing of electrons between atoms, resulting in partial electrical charges. This occurs mainly due to differences in electronegativity values between bonded atoms. Acrylamide displays chemical polarity because it contains a carbonyl group \((C=O)\), which is highly polar due to the oxygen atom's higher electronegativity compared to carbon.
Polarity affects a molecule’s behavior significantly:

• Dissolution: Polar molecules tend to dissolve well in polar solvents (like water) due to charge interactions.
• Intermolecular forces: Polarity leads to stronger dipole-dipole interactions and hydrogen bonding possibilities, influencing boiling points and solubilities.
• Reactivity: Polar molecules are more likely to engage in certain chemical reactions involving charge interactions.

Understanding polarity is essential for predicting how molecules like acrylamide will interact in various environments.

Chemical bond strength

Chemical bond strength refers to the energy required to break a bond between two atoms. In acrylamide, different bonds vary in strength. The carbon-carbon double bond \((C=C)\) is stronger than the carbon-carbon single bond \((C-C)\), primarily because double bonds include both sigma and pi bonds, whereas single bonds only have sigma bonds.
This attribute of bond strength is pivotal in:

• Reactivity: Compounds with higher bond strength typically require more energy to react, affecting reaction routes and rates.
• Stability: Stronger bonds contribute to the overall molecular stability, influencing storage and usage.
• Energy content: Higher energy bonds may release more energy upon breaking, relevant in biological systems and combustion processes.

Understanding these principles helps chemists and students predict how molecules like acrylamide behave and interact under various conditions.