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Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
All textbooksMullins 1st EditionCh. 3 - Alkanes and Cycloalkanes: Properties and Conformational AnalysisProblem 6b
Chapter 2, Problem 6b

How many hydrogens would you expect a 24-carbon compound from each of the following molecular classes to have?
(b) Alkene

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Step 1: Recall the general formula for alkenes. Alkenes are hydrocarbons that contain at least one double bond between carbon atoms. The general formula for an alkene is CₙH₂ₙ, where 'n' represents the number of carbon atoms.
Step 2: Identify the number of carbon atoms in the compound. The problem specifies that the compound contains 24 carbon atoms, so 'n' = 24.
Step 3: Substitute the value of 'n' into the general formula for alkenes. Using the formula CₙH₂ₙ, replace 'n' with 24 to determine the number of hydrogen atoms.
Step 4: Perform the substitution: CₙH₂ₙ becomes C₂₄H₂×₂₄. This simplifies to C₂₄H₄₈, indicating the molecular formula of the alkene.
Step 5: Note that this formula assumes the compound is a simple alkene with one double bond and no additional functional groups or rings. If the compound has multiple double bonds or is cyclic, the number of hydrogens would need to be adjusted accordingly.

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Key Concepts

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

Alkene Structure

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C). This double bond affects the overall structure and hydrogen count of the molecule. In alkenes, the presence of the double bond reduces the number of hydrogen atoms compared to alkanes, which are saturated hydrocarbons with only single bonds.
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Alkene Metathesis Concept 5

General Formula for Alkenes

The general formula for alkenes is CnH2n, where 'n' is the number of carbon atoms. This formula indicates that for every carbon atom in an alkene, there are typically two hydrogen atoms, adjusted for the presence of double bonds. For a 24-carbon alkene, this formula helps calculate the expected number of hydrogen atoms.
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Alkene Metathesis Concept 4

Degree of Unsaturation

Degree of unsaturation refers to the number of rings and multiple bonds in a compound. Each double bond or ring structure reduces the number of hydrogen atoms that can be attached to the carbon skeleton. For alkenes, the degree of unsaturation is one due to the presence of a double bond, which is crucial for determining the hydrogen count in the compound.
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The difference between saturated and unsaturated molecules.
Related Practice
Textbook Question

Choose the molecule in each pair you'd expect to have the higher boiling point. Explain your reasoning.

(a) eicosane ( C20H42) vs pentadecane

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Textbook Question

How many hydrogens would you expect a 24-carbon compound from each of the following molecular classes to have?

(a) Alkane

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Textbook Question

How many hydrogens would you expect a 24-carbon compound from each of the following molecular classes to have?

(c) Alkyne

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Textbook Question

What is the hybridization of carbon in each of the following molecules?

(a)

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Textbook Question

What is the hybridization of carbon in each of the following molecules?

(d)

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Textbook Question

Draw the molecular orbital picture for propane. Your picture should clearly show the shape and hybridization of the carbons. Label all σ bonds.

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