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Ch.7 - Covalent Bonding and Electron-Dot Structures
McMurry - Chemistry 8th Edition
McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook
All textbooksMcMurry 8th EditionCh.7 - Covalent Bonding and Electron-Dot StructuresProblem 11
Chapter 7, Problem 11

The structure for the DNA base cytosine is shown.
Chemical structure of the DNA base cytosine with resonance structures options a, b, c, d.
Which of the following is not a resonance structure of cytosine? (LO 7.13) (a)
(b)
(c)
(d)

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1
Identify the structure of cytosine and compare it with the given structure of thymine.
Recall the rules for drawing resonance structures, which include the movement of electrons but not atoms.
Examine each resonance structure option (a, b, c, d) for cytosine and determine if they follow the resonance rules.
Check if any of the options involve breaking the resonance rules, such as moving atoms or violating the octet rule.
Identify the option that does not represent a valid resonance structure of cytosine.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Resonance Structures

Resonance structures are different ways of drawing the same molecule that illustrate the delocalization of electrons. They are used to represent molecules where the actual structure is a hybrid of these forms, providing a more accurate depiction of electron distribution. In the case of cytosine, resonance structures help explain the stability and reactivity of the molecule.
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Cytosine Structure

Cytosine is one of the four main bases found in DNA and RNA, characterized by its pyrimidine ring structure. It contains nitrogen and oxygen atoms, which play crucial roles in hydrogen bonding and base pairing. Understanding its structure is essential for recognizing how it interacts with other nucleobases and contributes to the genetic code.
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Identifying Non-Resonance Structures

Identifying non-resonance structures involves recognizing which proposed structures do not accurately represent the electron distribution of the molecule. This requires knowledge of the rules governing resonance, such as the conservation of atom connectivity and the placement of electrons. Analyzing the given options critically helps in determining which structure deviates from the valid resonance forms.
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Related Practice
Textbook Question
The compounds below are paired with a type of bonding. Which type of bonding is incorrectly classified? (LO 7.5) (a) Rb2O (polar covalent) (b) SO2 (polar covalent) (c) O3(nonpolar covalent)(d) KBr (ionic) (e) HF (polar covalent)
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Textbook Question
Which compound is a solid at room temperature? (LO 7.8)(a) H2O(b) Na2S (c) SO3 (d) Cl2
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Textbook Question

Which of the following pairs represent resonance structures? (LO 7.13) (a)(b)(c)

Textbook Question
What is the best prediction for the carbon–oxygen bond length in the carbonate anion, CO3 2-? (LO 7.14)Data for average carbon-oxygen bond lengths: (a) 143 pm (b) 132 pm(c) 121 pm(d) 118 pm
Textbook Question
Which is the best electron-dot structure for the thiosulfate ion (S2O3 2-) based on the rules of formal charge? (LO 7.16)(a) (b) (c) (d)
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Textbook Question

Use formal charge to select which resonance structure makes the largest contribution to the resonance hybrid. (LO 7.16) (a) Structure I (b) Structure II (c) Structure III (d) All structures are equivalent and make the same contri-bution to the resonance hybrid. (I)

(II)

(III)