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My Packs: UWO (CHEM 1301) > Chapter 5: 5.3 Alkanes, Cycloalkanes, and Alkenes > Flashcards

Chapter 5: 5.3 Alkanes, Cycloalkanes, and Alkenes Flashcards

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1
Q

Define:
Alkanes

A

Straight or branched-chained compounds containing C and H atoms and only single carbon-carbon bonds

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2
Q

State the general formula for acyclic alkanes

A

C(n)H(2n+2)

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3
Q

Define:
Homologous series

A

Compounds that are structurally related to one another

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4
Q

Define:
Constitutional isomers

A

Compounds with the same molecular formula but different bonding sequences

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5
Q

What are constitutional isomers also known as?

A

Structural isomers

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6
Q

True or False:
Physical properties of alkanes change with molecular size

A

True

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7
Q

True or False:
Constitutional isomers have the same chemical properties

A

False, they have different chemical and physical properties

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8
Q

What are the 3 common ways of representing 3D Structures?

A

Dot-line-wedge formulas
Sawhorse projections
Newman projections

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9
Q

Describe dot-line-wedge formulas

A

Lines represent bonds in the plane of the paper
Dotted lines represent bonds behind the plane of the paper
Wedged lines represent bonds in front of the plane of the paper

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10
Q

Describe sawhorse projections

A

Drawn in the shape of a sawhorse using only plain lines

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11
Q

What molecules are sawhorse projections used for?

A

Only for simple molecules

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12
Q

Describe Newman projections

A

The molecule is viewed along the C-C axis bonds are drawn in front of and along the edge of a circle

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13
Q

Define:
Conformations

A

Transient (non-permanent) spatial arrangements of atoms in a molecule produced by rotations about single bonds

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14
Q

Can conformations occur around double bonds?

A

No, as they cannot spin around double bonds

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15
Q

What are the two key conformations of alkanes?

A

Staggered
Eclipsed

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16
Q

Describe staggered conformation

A

The C-H- bonds in front bisect the H-C-H bond angles in the back (C-H bonds are not aligned)

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17
Q

Describe eclipsed conformation

A

All C-H bonds are aligned

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18
Q

Eclipsed conformation is ______ in energy because:

A

Higher
Steric repulsion between the front and rear H atoms

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19
Q

Are conformations the same as isomers?

A

No, conformations can switch seamlessly back and forth
Isomers are unique

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20
Q

Since the energy difference between staggered and eclipsed conformations are relatively _____, they interconvert at a ____ rate

A

Small
Fast

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21
Q

What is the angle between methyl groups in a Newman projection known as?

A

Dihedral angle

22
Q

When there are multiple staggered conformations, what is the one lowest in energy called?

A

Anti conformer

23
Q

When there are multiple staggered conformations, what are the ones higher in energy than the anti conformer called?

A

Gauche conformers

24
Q

Define:
Cycloalkanes

A

Hydrocarbons containing a ring of carbon atoms connected by single C-C bonds

25
Q

What is the general formula for cycloalkanes?

A

C(n)H(2n)

26
Q

Of all cycloalkanes, which one is the most common?

A

Cyclohexane

27
Q

What are the two distinct conformations that cyclohexane has?

A

Boat
Chair

28
Q

Why is the boat conformation of cyclohexane present in very small amounts?

A

The flagpole interactions due to eclipsed conformations make it not favorable

29
Q

Describe conformations for C-H bonds in a chair conformation

A

All C-H bonds on adjacent carbons are staggered

30
Q

Define:
Axial substituents

A

The six substituents directed straight up or down in chair conformation of cyclohexane

31
Q

Define:
Equatorial susbtituents

A

The other six substituents directed laterally or outward in chair conformation of cyclohexane

32
Q

Large groups prefer to be in an ___________ position.
Why?

A

Equatorial
Equatorial substituents are less crowded since they are more distant from other substituents in the ring

33
Q

Define:
Constitutional isomers

A

Isomers that share the same molecular formula but cannot be formed by rotating one to form the other

34
Q

Define:
Stereoisomers

A

Cis-trans isomers
Occurs when a cycloalkane ring has two or more non-hydrogen substituents on different ring carbons, they can occupy two different positions relative to the approximate ring plane

35
Q

What is the difference between stereoisomers and constitutional isomers?

A

Both have the same molecular formulas
Constitutional isomers have a different bond order

36
Q

Describe cis isomers

A

Two substituents on the same (cis) side of the ring plane

37
Q

Describe trans isomers

A

Two substituents on opposite (trans) sides of the ring plane

38
Q

Stereoisomers have same _________ ________ and the same _______ ________ (____________), but have different, non-interconverting __ __________

A

Molecular formula
Bonding sequence (connectivity)
3D structures

39
Q

Do cis-trans isomers interconvert at room temperature?

A

No

40
Q

Define:
Alkenes

A

Hydrocarbons with one or more double bonds

41
Q

State the general formula of homologous alkenes with one C=C double bond

A

C(n)H(2n)

42
Q

Define:
Alkynes

A

Hydrocarbons with one or more triple bonds

43
Q

State the general formula of homologous alkynes with CC triple bond

A

C(c)H(2n-2)

44
Q

What does it mean for a hydrocarbon to be saturated?

A

It contains the maximum possible number hydrogen atoms (2n+2)

45
Q

Select the unsaturated hydrocarbon(s) from below:
Alkanes
Alkenes
Alkynes

A

Alkenes and alkynes

46
Q

The removal of _ H atoms represent ___ unit of unsaturation

A

2
One

47
Q

What is the structure of an alkene? Explain

A

Planar structure
The C=C bond is bonded to three atoms and is sp2 (planar), the remaining p orbital overlap to form a pi bond which cannot rotate, leaving it in planar

48
Q

What is the structure of an alkyne? Explain

A

Linear structure
The CC triple bond is bonded to two atoms and is sp (linear), the remaining 2 p orbitals give rise to 2 pi orbitals which cannot rotate, leaving it in linear

49
Q

What is a potential consequence of the inability of the carbon-carbon double bond in alkenes to rotate?

A

Geometric isomerism

50
Q

True or False:
cis-trans arrangements can occur in rings

A

Not exactly
In rings with seven members or less, a double bond within the ring can have only the cis geometry because the trans arrangement would be too strained

51
Q

State the formula for maximum possible number of cis-trans isomers

A

2^n
n is the number of double bonds

My Packs: UWO (CHEM 1301) (17 decks)

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