The molecule shown here is styrene, C8H8, a benzene derivative that is used to make a number of polymers, including polystyrene. The shorthand notation for the benzene ring (described in Section 8.6) is used. Three of the carbon–carbon bonds are numbered in the structure. a. Which of the three bonds is the strongest? b. Which of the three bonds is the longest? c. Which of the three bonds is best described as halfway between a single and a double bond? [Sections 8.6 and 8.8]
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Step 1: Understand the structure of styrene, C8H8. It consists of a benzene ring (a six-carbon ring with alternating double bonds) and a vinyl group (CH=CH2).
Step 2: Identify the three carbon-carbon bonds in question. Typically, these would be the bonds within the benzene ring and the bond connecting the vinyl group to the benzene ring.
Step 3: Recall that in a benzene ring, the carbon-carbon bonds are resonance hybrids, meaning they are not true single or double bonds but are somewhere in between. This affects their strength and length.
Step 4: Compare bond types: Single bonds (C-C) are generally longer and weaker than double bonds (C=C). In benzene, the bonds are intermediate in length and strength due to resonance.
Step 5: Determine the characteristics of each bond: The bond connecting the vinyl group to the benzene ring is a true single bond, making it the longest. The bonds within the benzene ring are resonance-stabilized, making them stronger than a single bond but weaker than a double bond, and they are best described as halfway between a single and a double bond.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Bond Strength
Bond strength refers to the energy required to break a bond between two atoms. In organic molecules, bonds can vary in strength based on their type; for example, double bonds are generally stronger than single bonds due to the presence of two shared electron pairs. Understanding bond strength is crucial for determining which bond in styrene is the strongest.
Bond length is the distance between the nuclei of two bonded atoms. Typically, single bonds are longer than double bonds because the additional electron pair in a double bond pulls the atoms closer together. Analyzing the bond lengths in styrene helps identify which bond is the longest among the three specified.
Resonance is a concept in chemistry that describes the delocalization of electrons in molecules where bonds can be represented by multiple structures. In styrene, the carbon-carbon bond that is halfway between a single and a double bond is indicative of resonance, where the bond characteristics are averaged due to the presence of alternating single and double bonds in the benzene ring.
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