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Ch.1 - Structure and Bonding
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.1 - Structure and BondingProblem 56a,b
Chapter 1, Problem 56a,b

a. Draw the structure of cis-CH3CH=CHCH2CH3 showing the pi bond with its proper geometry.
b. Circle the six coplanar atoms in this compound.

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1
Identify the structure of the compound: cis-CH3CH=CHCH2CH3. This is a pentene molecule with a double bond between the second and third carbon atoms.
Draw the carbon chain: Start by drawing a five-carbon chain. Label the carbons as C1, C2, C3, C4, and C5 from left to right.
Add the double bond: Place a double bond between C2 and C3. Since the compound is 'cis', ensure that the CH3 group on C1 and the CH2CH3 group on C4 are on the same side of the double bond.
Show the geometry of the pi bond: The double bond consists of a sigma bond and a pi bond. The pi bond is formed by the sideways overlap of p orbitals, which are perpendicular to the plane of the sigma bond. Draw the p orbitals on C2 and C3 to illustrate the pi bond.
Circle the six coplanar atoms: In a cis-alkene, the atoms involved in the double bond and the atoms directly attached to them are coplanar. Circle the atoms: C1, C2, C3, C4, and the two hydrogen atoms attached to C2 and C3, as these are the six coplanar atoms in the molecule.

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Key Concepts

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

Cis-Trans Isomerism

Cis-trans isomerism is a form of stereoisomerism where the relative orientation of functional groups differs around a double bond. In cis isomers, similar groups are on the same side, while in trans isomers, they are on opposite sides. This affects the molecule's geometry and physical properties.
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Is the following cyclohexane cis or trans?

Pi Bond Geometry

Pi bonds are formed by the sideways overlap of p orbitals, creating a region of electron density above and below the plane of the atoms involved. In alkenes, the pi bond restricts rotation, resulting in a planar geometry around the double bond, which is crucial for understanding molecular shape and reactivity.
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Coplanar Atoms

Coplanar atoms are atoms that lie in the same geometric plane. In molecules with double bonds, such as alkenes, the atoms directly involved in and adjacent to the double bond are typically coplanar due to the rigidity imposed by the pi bond, affecting the molecule's overall shape and interactions.
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Related Practice
Textbook Question

Circle the coplanar atoms in the following structure:

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Textbook Question

Which of the following compounds show cis-trans isomerism? Draw the cis and trans isomers of the ones that do.

(a) CH3CH=CHCH3

(b) CH3C≡CCH3

(c) CH2=C(CH3)2

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Textbook Question

Draw orbital pictures of the pi bonding in the following compounds:

f. CH3CH=NCH=C=O

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Textbook Question

Draw orbital pictures of the pi bonding in the following compounds:

a. CH3COCH3

b. HCN

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Textbook Question

In pent-2-yne (CH3CCCH2CH3), there are four atoms in a straight line. Use dashed lines and wedges to draw a three-dimensional representation of this molecule, and circle the four atoms that are in a straight line.

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Textbook Question

Draw orbital pictures of the pi bonding in the following compounds:

e. CH3CH=C=CHCH3

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