Chapter 4 Flashcards

Alkanes

1
Q

Define saturated hydrocarbon

A

Hydrocarbons that contain only single bonds between carbon atoms.

  • Simplest form of hydrocarbons
  • Saturated bc each carbon atom is bonded to as many hydrogen atoms as possible
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2
Q

Define alkane

A

saturated hydrogen carbons with sigma (single bonds)

  • can be in a chain or ring
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3
Q

What are the two types of alkanes?

A

Acyclic alkanes and cycloalkanes

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4
Q

Define acyclic alkanes

A

Formula= CnH2n+2

Linear and branched chains

  • saturated hydrocarbon bc max number of hydrogens
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5
Q

Define cycloalkanes

A

Formula = CnH2n

  • Makes a ring
  • have 2 fewer Hydrogens than acyclic
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6
Q

What is an alkane’s hybridization?

A

Sp3 and tetrahedral geometry

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7
Q

Define isomers

A

Two different compounds with the same molecular formula

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8
Q

What are the two main types of isomers?

A

Constitutional isomers and stereoisomers

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9
Q

Define constitutional isomers

A

molecules that differ in the way the atoms are connected to each other

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10
Q

Define alkyl group

A

Formed by removing one hydrogen from an alkane

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11
Q

Are alkanes polar or nonpolar?

A

Nonpolar

  • they only have c-c and c-h bonds
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12
Q

Do alkanes have lower or higher mp’s and bp’s than more polar compounds?

A

Lower mp and bp bc of less intermolecular forces

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13
Q

How does the mp and bp in alkanes increase?

A

Increasing the number of carbons increases surface area which increases mp and bp

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14
Q

Does branching on isomers increase or decrease bp?

A

Branching decreases bp bc less surface area

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15
Q

Does cymmetry increase or decrease mp?

A

Symmetry increases mp

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16
Q

Define stereochemistry

A

The 3D structure of molecules

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17
Q

Where does rotation occur in organic molecules?

A

Around c-c sigma bonds

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18
Q

Define conformations

A

Different arrangements of atoms that are involved by rotation about single bonds

19
Q

What are the two types of conformations?

A

Eclipsed and staggered conformations

20
Q

Define eclipsed conformations

A

C-H bond on one carbon is directly aligned with the C-H bond of the adjacent carbon

21
Q

Define staggered conformations

A

The C-H bond of one carbon bisects the H-C-H bond angle on the adjacent carbon

22
Q

Define dihedral angle

A

The angle that separates a bond on one atom from a bond on an adjacent atom

23
Q

Does a stable molecule have higher or lower energy?

A

Lower energy, it’s not excited

24
Q

Are staggered or eclipsed conformations more stable?

A

Staggered conformations are more stable (lower in energy)

25
Define torsional energy
The difference between staggered and eclipsed conformations
26
Define torsional strain
An increase in the energy caused by eclipsing interactions
27
Define anti rotations
Staggered conformation with two larger groups 180 degrees from each other
28
Define gauche rotations
Staggered conformation with two larger groups 60 degrees from each other
29
Define steric strain
An increase in energy resulting when atoms are forced too close to one another
30
Are gauche or anti conformations more stable?
Anti conformations are more stable (lower in energy) bc less steric strain
31
Define angle strain
An increase in energy when tetrahedral bond angles deviate from the optimum angle of 109.5 degrees
32
What is the most common ring size in naturally occurring compounds?
Cyclohexanes | - 6 carbons
33
What is the most stable form of a cyclohexane?
The chair form - all C-C bonds are 109.5 (ideal) - H's are staggered and not eclipsed
34
What is the structure of a cyclohexane?
- 3 up carbons and 3 down carbons - axial H's (go up and down) - equatorial H's (located in the plane of the ring)
35
What is a conformation of the chair cyclohexane?
The boat cyclohexane - the down carbon on the end flips up
36
How many chair conformations of cyclohexanes exist?
2 with same stability - up carbons -> down - axial H's -> equatorial
37
Are chair or boat cyclohexanes more stable?
Chair bc more staggered and less torsional strain
38
Is there more room for large groups on axial or equatorial positions?
Equatorial bs less steric interactions
39
Define stereoisomers
Isomers that differ only in the way the atoms are oriented in space
40
What are the two types of stereoisomers?
Cis - two groups on same side of ring trans - two groups on opposite sides of the ring
41
In monosubstituted cyclohexanes, is axial or equatorial more favored?
Equatorial
42
In 1,2-disubstituted cyclohexanes is cis or trans more stable?
Trans bc 2 equatorial sites
43
In 1,3-disubstituted cyclohexanes is cis or trans more stable?
Cis bc 2 equatorial sites
44
In 1,4-disubstituted cyclohexanes is cis or trans more stable?
Trans bc 2 equatorial sites