Given the line-angle drawings shown, answer the following questions:
(i) How many carbons are in each molecule?
(ii) How many hydrogens are at the circled carbon?
(iii) Is the indicated (→) carbon or 1° , 2°, 3°, or 4°?
(c)

Verified step by step guidance

Step 1: Count the total number of carbons in the molecule. In a line-angle drawing, each vertex represents a carbon atom, and each line represents a bond. Carefully trace the structure and count all the carbons, including those at the ends of lines and vertices.

Step 2: Determine the number of hydrogens attached to the circled carbon. The circled carbon is part of a double bond (alkene). Recall that a carbon in a double bond typically has fewer hydrogens due to the presence of π-bonds. Use the rule that carbon forms four bonds in total, and subtract the number of bonds already shown to find the number of hydrogens.

Step 3: Analyze the indicated carbon (marked with an arrow) to determine its degree (1°, 2°, 3°, or 4°). The degree of a carbon is based on the number of other carbons directly attached to it: 1° (primary) has one carbon attached, 2° (secondary) has two carbons attached, 3° (tertiary) has three carbons attached, and 4° (quaternary) has four carbons attached.

Step 4: Verify the connectivity of the molecule to ensure accuracy in your analysis. Double-check the structure to confirm the number of carbons, hydrogens, and the degree of the indicated carbon.

Step 5: Summarize your findings for each part of the question: (i) total number of carbons, (ii) number of hydrogens at the circled carbon, and (iii) degree of the indicated carbon.

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Key Concepts

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

Line-Angle Structures

Line-angle structures, also known as skeletal formulas, are a simplified way of representing organic molecules. In these drawings, each vertex represents a carbon atom, and the lines between them represent bonds. Hydrogen atoms are typically omitted for carbon atoms, as they are implied based on carbon's tetravalency. Understanding how to interpret these structures is crucial for determining the number of carbons and hydrogens in a molecule.

Degree of Carbon

The degree of a carbon atom refers to the number of other carbon atoms it is directly bonded to. A carbon can be classified as primary (1°) if it is attached to one other carbon, secondary (2°) if attached to two, tertiary (3°) if attached to three, and quaternary (4°) if attached to four. This classification is important for understanding the reactivity and stability of the carbon atom in organic reactions.

Hydrogen Count at a Carbon

The number of hydrogen atoms bonded to a carbon atom can be determined by considering the carbon's tetravalency, which states that carbon forms four bonds. The number of hydrogens attached to a specific carbon can be calculated by subtracting the number of other atoms (like carbons or functional groups) bonded to it from four. This concept is essential for accurately answering questions about the hydrogen count at specific carbons in a molecule.

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