Ch. 3: An Introduction to Organic Compounds Flashcards
1
Q
What is an alkane?
A
a compound composed only of carbon and hydrogen atoms and contain only single bonds
2
Q
What is a hydrocarbon?
A
compounds that contain only carbon and hydrogen atoms
3
Q
What is a straight-chain alkane?
A
alkanes in which the carbons form a continuous chain with no branches
4
Q
CH4
A
methane
CH4
5
Q
C2H6
A
ethane
CH3CH3
6
Q
C3C8
A
propane
CH3CH2CH3
7
Q
C4C10
A
butane
CH3CH2CH2CH3
8
Q
C5H12
A
pentane
CH3(CH2)3CH3
9
Q
C6H14
A
hexane
CH3(CH2)4CH3
10
Q
C7H16
A
heptane
CH3(CH2)4CH3
11
Q
C8H18
A
octane
CH3(CH2)6CH3
12
Q
C9H20
A
nonane
CH3(CH2)7CH3
13
Q
C10H22
A
decane
CH3(CH2)8CH3
14
Q
What is a homologous series?
A
a family of compounds in which each member differs from the one before it in the series by one methylene (CH2) group. the members of a homologous group are called homologues.
15
Q
What’s the general molecular formula for an alkane?
A
CnH2n+2, where n is any positive integer
16
Q
How many possible structures are there for methane, ethane, and propane?
A
one possible structure for each
17
Q
How many possible structures are there for butane?
A
two possible structures
18
Q
What are constitutional isomers?
A
compounds such as butane and isobutane that have the same molecular formula but differ in the way atoms are connected
19
Q
What is an “iso” structural unit?
A
20
Q
How many possible structures are there for pentane?
A
three possible structures
21
Q
How many possible structures are there for hexane?
A
five constitutional isomers with molecular formula C6H14
22
Q
How many possible structures are there for heptane?
A
nine alkanes with molecular formula C7H16
23
Q
How are alkyl groups named?
A
Alkyl groups are named by replacing the “ane” ending of the alkane with “yl”
24
Q
What is an alkyl subsituent?
A
the result of removing a hydrogen from an alkane
25
What happens if an H in an alkane is replaced by an OH?
the compound becomes an alcohol
26
What happens if an H in an alkane is replaced by an NH2?
the compound becomes an amine
27
What happens if an H in an alkane is replaced by a halogen?
the compound becomes an alkyl halide
28
What happens if an H in an alkane is replaced by an OR?
the compound becomes an ether
29
What is a propyl group?
the result of when a H is removed from a primary carbon of propane
30
What is a primary carbon?
a carbon bonded to only one other carbon
31
What is an isopropyl group?
the result of when a H is removed from the secondary carbon of propane
32
What is a secondary carbon?
a carbon bonded to two other carbons
33
What is a butyl group?
have a hydrogen removed from a primary carbon
34
What is an isobutyl group?
have a hydrogen removed from a primary carbon
35
What is a sec-butyl group?
has a hydrogen removed from a secondary carbon
36
What is a tert-butyl group?
has a hydrogen removed from a tertiary carbon
37
What is a tertiary carbon?
A carbon bonded to three other carbons
38
What is a primary hydrogen?
a hydrogen attached to a primary carbon
39
What is a secondary hydrogen?
a hydrogen attached to a secondary carbon
40
what is a tertiary hydrogen?
a hydrogen attached to a tertiary carbon
41
Can you use the prefix "sec" like with "sec-butyl" for other compounds that have a CH3 group on the secondary C?
No! Besides sec-butyl, using "sec" wouldn't be correct terminology because other compounds like pentane may have multiple secondary carbons
42
What can the prefix "tert" be used for?
both tert-butyl and turt-pentyl compounds because each of these substituent names describes only one alkyl group. With that in mind, tert-hexyl cannot be used because it would describe two different alkyl groups
43
What is the only isoalkyl compound without the substituent on the primary C?
isopropyl alcohol, it has its substituent on a secondary carbon
44
methyl
45
ethyl
46
propyl
47
isopropyl
48
butyl
49
isobutyl
50
sec-butyl
51
tert-butyl
52
pentyl
53
isopentyl
54
hexyl
55
isohexyl
56
Draw the structure of a compound with no secondary carbons.
57
Draw the structures and name the four constitutional isomers with molecular formula C4H9Br
58
What is a parent hydrocarbon and how does it affect the name of an alkane?
The number of carbons in the longest continuous carbon chain. The name that indicates the number of carbons in the parent hydrocarbon becomes the alkane's "last name."
59
Where is the name of the alkyl substituent placed in relation to the parent hydrocarbon?
The name of any alkyl substituent attached to the parent hydrocarboin is placed in front of the name of the parent hydrocarbon. Both names are joined into one word, preceded by a hyphen that connects the substituent's number with its name.
60
How does the alkyl substituent affect the numbering of the carbons in the parent chain?
The carbons in the parent chain are numbered in the direction that gives the substituent as low a number as possible.
61
If there are more than one substituents attached to the parent hydrocarbon, how do you decide the chain is numbered?
The chain is numbered in the direction that produces a name containing the lowest of the possible numbers. The substituents are listed in alphabetical order, with each substituent preceded by the appropriate number.
62
How does it affect the name of your compound if two or more of the substituents are the same?
the prefixes "di," "tri," and "tetra" are used to indicate how many identical substituents the compound has. The numbers indicating the locations of the identical substituents are listed together, separated by commas.
63
Are prefixes considered or ignored in alphabetizsing substituents?
ignored
64
If numbering in either direction on a parent hydrocarbon leads to the same lowest number for one of the substituents, how do you number the chain?
the chain is numbered in the direction that gives the lowest possible number to one of the remaining substituents
65
If the same substituent numbers are obtained in both directions, how do you decide which groups receives which number?
the first group receives the lower number (by alphabetic order basically)
66
How do you name a complex substituent?
1. identify the complex substituent in your alkane
2. you can number the number-1 carbon of the substituent, it's the one attached to the parent hydrocarbon, then identify the mini parent chain within the substituent
3. identify what's attached to the carbons in the step parent chain
4. name these as they are, remembering to add a number before each name and alphabetizing it
67
If you a prefix within a complex substituent, is it considered in the alphabetization of the name?
Yes!
68
If a compound has two or more chains of the same length, how do you identify the parent hydrocarbon?
the parent hydrocarbon is the chain with the greatest number of substituents
69
What are the steps for writing a compound's systematic name?
1. determine the parent hydrocarbon
2. identify the substituents
3. number the chain according to the substituents (may have to be done after 4.)
4. identify what the substituents are
5. put together the name of the compound
70
Draw the structure and give the systemic name for a compound with molecular formula C5H12 that has only primary and secondary hydrogens.
71
Draw the structure and give the systemic name for a compound with molecular formula C5H12 that has only primary hydrogens.
72
Draw the structure and give the systemic name for a compound with molecular formula C5H12 that has only one tertiary hydrogen.
73
Draw the structure and give the systemic name for a compound with molecular formula C5H12 that has only two secondary hydrogens.
74
What is a cycloalkane?
alkanes with their carbon atoms arranged in a ring
75
What is the general molecular formula of a cycloalkane?
CnH2n
76
What are the rules for naming cycloalkanes?
1) the ring is the parent hydrocarbon unless the substituent has more carbons than the ring. In that case the substituent is the parent hydrocarbon and the ring is the substituent
2) If the ring has two different substituents, they are listed in alphabetical order and the number-1 position is given to the substituent listed first
3) If the ring has >2 substituents then they are listed in alphabetical order and the substituent given the number-1 position is the one that results in a second substituent getting as low a number as possible. If the two have the same low number, then consider the lowest number for the third substituent, and so on.
77
What is an alkyl halide?
a compound in which a hydrogen of an alkane has been replaced by a halogen.
78
What is a primary alkyl halide?
has a halogen attached to a primary carbon
79
What is a secondary alkyl halide?
has a halogen attached to a secondary carbon
80
What is a tertiary alkyl halide?
has a halogen attached to a tertiary carbon
81
What are the halogens?
Br, Cl, F, I, At, Ts
82
What are the common names of alkyl halides?
consists of the name of the alkyl group, followed by the name of the halogen with the ending "ine"
83
What are the systematic names of alkyl halides?
alkyl halides are named as substituted alkanes and the prefixes for halogens end with "o"
84
What is a symmetrical ether?
A compound with an oxygen attached to two alkyl groups is called an ether.
In a symmetrical ether, the two alkyl groups are the same (R and R)
85
What is an unsymmetrical ether?
A compound with an oxygen attached to two alkyl groups is called an ether.
In an unsymmetrical ether, the two alkyl groups are different (R and R')
86
How do you find the common name of an ether?
consists of the names of the two alkyl groups (in alphabetical order) followed by the word "ether"
87
How do you name the substituent of an ether?
replace the "yl" with "oxy"
88
What is an alcohol?
a compound in which a hydrogen of an alkane has been replaced by an OH group
89
What is a primary alcohol?
has an OH group attached to a primary carbon
90
What is a secondary alcohol?
has an OH group attached to a secondary carbon
91
What is a tertiary alcohol?
has an OH group attached to a tertiary carbon
92
How do you find the common name of an alcohol?
consists of the name of the alkyl group to which the OH group is attached, followed by the word "alcohol"
93
What is a functional group?
the center of reactivity in an organic molecule
94
How do you give the systematic name of an alcohol?
the number immediately precedes the name of the parent hydrocarbon or immediately preceding the suffix. Replace the end of the name of the parent hydrocarbon with "ol"
95
What are the 6 rules for naming a compound with a functional group suffix?
1) the parent hydrocarbon is the longest continuous chain that contains the functional group
2) the parent hydrocarbon is numbered in the direction that gives the functional group suffix the lowest number possible
3) If there are two OH groups, the suffix "diol" is added to the name of the parent hydrocarbon
4) If there is a functional group suffix and a substituent, the functional group suffix gets the lowest possible number
5) If counting in either direction gives the same number for the functional group suffix, then the chain is numbered in the direction that gives a substituent the lowest number possible
6) If there is more than one substituent, the substituents are listed in alphabetical order
96
What is an amine?
a compound in which one of more hydrogens of ammonia have been replaced by alkyl groups
97
What is a primary amine?
has one alkyl group attached to the nitrogen
98
What is a secondary amine?
has two alkyl groups attached to the nitrogen
99
What is a tertiary amine?
has three alkyl groups attached to the nitrogen
100
How do you write the systematic name of an amine?
the "e" at the end of the name of the parent hydrocarbon is replaced by "amine". A number identifies the carbon to which the nitrogen is attached, and the name of any alkyl group is preceded by "N" to indicate the group is bonded to a nitrogen rather than a carbon
101
What is a quaternary ammonium salt?
nitrogen compounds with four alkyl groups attached to the nitrogen, thereby giving the nitrogen a positive formal charge
102
How is the C--X bond of an alkyl halide formed and how does it change based on the halogen "X"
the C--X bond is formed from the overlap of an sp3 orbital of carbon with an sp3 orbital of the halogen. The C--X bond becomes longer and weaker as the size of the halogen increases because the electron density of the orbital decreases with increasing volume
103
What is the geometry of an oxygen in an alcohol?
It is bent like in water. It can be thought of as a water molecule with an alkyl group in place of one of the hydrogens
104
What is the geometry of an oxygen in an ether?
It is bent like in water. It can be thought of as a water molecule with two alkyl groups in place of the hydrogens.
105
Explain the geometry of the nitrogen in an amine?
Tetrahedral, the same geometry of a nitrogen in ammonia.
106
Are alkane bonds polar or nonpolar? What intermolecular forces are present in them?
nonpolar, they contain only C and H. The only forces present are induced-dipole-induced-dipole interactions (LDFs).
107
What are london dispersion forces?
Induced-dipole-induced-dipole interactions, the weakest if all the attractive forces. The magnitude of LDFs that hold alkane molecules together depends on the area of contact between the molecules. As the molecular weight of an alkane increases, the BP increases because each additional CH2 group increases the area of contact between the molecules.
108
What are branched alkanes?
Branched alkanes are isomers of straight-chain alkanes, They have the same number of C atoms, but they are different compounds with different physical and chemical properties. Branching lowers a compound's BP by reducing the area of contact (basically makes it easier to break apart)
109
What is the order of intermolecular forces from strongest to weakest?
1) ion-dipole force
2) hydrogen bond
3) dipole-dipole force
4) London-dispersion force
110
As the molecular weight of a series of ethers, alkyl halides, alcohols, and amines increases, does the boiling point increase or decrease?
increase, because of the increase of LDFs
111
Are the C--Z bonds in ethers, alkyl halides, alcohols, and amines polar or nonpolar?
polar
112
What are dipole-dipole interactions?
Molecules with polar bonds are attracted to one another because they can align themselves in such a way that the positive end of one dipole is adjacent to the negative end of another dipole.
113
Wha is polarizability?
indicated how readily an electron cloud can be distorted to create a strong induced dipole
114
How does the size of an atom affect the polarizability of a compound?
The larger the atom, the more loosely it holds the electrons in its outermost shel and the more they can be distorted
115
What is a hydrogen bond?
A special kind of dipole-dipole interaction that occurs between a hydrogen that is attached to an oxygen, a nitrogen, or a fluorine and a lone pair of an oxygen, nitrogen, or a flourine in another molecule
116
Does an alcohol or an ether have a lower boiling point and why?
Alcohol because even though H-bonds don't take that much energy to break, there are many such bonds holding alcohol molecules together and that takes a lot of extra energy
117
Why does a primary amine have a higher BP than a secondary or tertiary amine?
When we compare amines with the same molecular weight, the primary amine has a higher BP than the secondary amine and the secondary higher than the tertiary because primaries have stronger dipole-dipole interactions (higher H-bonding)
118
What is melting point and what is it influenced by?
the MP of a compound is the temperature at which its solid form is converted into a liquid.
MP is influenced by molecular weight and packing. Typically, as the molecular weight increases so do the MPs of alkanes. Also influenced by packing in the crystal lattice. The tighter the fit, the more energy required to break the lattice and melt the compound.
119
Do even number straight-chain alkanes have a higher or lower MP than an odd-numbered straight-chain alkane?
Even numbers have higher MPs because they can pack tighter. Odd-numbered ones pack less tightly because the molecules can lie next to each other with a methyl group on the end of one facing and repelling the methyl group on the end of the other, thus increasing the average distance between the chains
120
Why do polar compounds dissolve in polar solvents?
Because a polar solvent such as water has partial charges that can interact with the partial charges one another compound
121
Why do nonpolar solutes dissolve in nonpolar solvents?
because the LDFs between solvent and solute molecules are about the same as those between solvent molecules or those between solute molecules
122
Are alkanes polar or nonpolar?
nonpolar
123
Are alcohols polar or non-polar?
It depends on the size of the alkyl group. As the alkyl group increases i size, becoming a more significant fraction of the entire alcohol molecule, the compound becomes less and less soluble in water. In other words, the molecule becomes more and more like an alkane. Generally, molecules with fewer than four Cs are soluble in water, and alcohols with more than 4 are insoluble in water. It also depends on the structure of the alkyl group. Alcohols with branched alkyl groups are more soluble in water than unbranched because branching minimizes the contact surface of the nonpolar portion of the molecule.
124
Are branched or unbranched alcohols more soluble?
Branching minimizes the contact surface of the non-polar portion of the molecule. So branched alkyl groups are more soluble than unbranched alkyl groups. Thus, tert-butyl alcohol is more soluble than n-butyl alcohol in water.
125
How do you know if an ether is soluble or nonsoluble?
The oxygen of an ether, like the oxygen of an alcohol can drag only about three carbons into solution in water.
125
How do you know if an amine is soluble in water?
Low-molecular-weight amines are soluble in water because primary, secondary, and tertiary amines have a lone pair they use to form a H-bond. Primary amines are more soluble than secondary amines with the same number of carbons because primary amines have two Hs that can engage in H-bonding with water. Tertiary amines do not have Hs to donate for H-bonds so they are less soluble in water than are secondary amines with the same number of carbons.
126
How do you know if an alkyl halide is soluble in water?
Alkyl halides have some polar character, but only alkyl flourides have an atom that can form a hydrogen bond with water so they're the most soluble in water. The other alkyl halides are less soluble in water than ethers or alcohols with the same number of carbons.
127
What are conformational isomers?
the different spatial arrangements of the atoms that result from rotation about a single bond are conformers
128
What are Newman projections?
Represents the 3D structures that result from rotation about a sigma bond. A Newman projection assums that the viewer is looking along the longitudinal axis of a particular C--C bond. The carbon in front is represented by a point and the C in the back by a circle.
129
What is a staggered conformer?
Represents two extremes because rotation about a C--C bond can produce an infinite number of conformers between twi extremes.
A staggered conformer is more stable, and therefore, lower in energy than an eclipsed conformer. Thus, rotation about a C--C bond is not completely free because an energy barrier must be overcome when rotation occurs. However, the energy barrier is small enough to allow continuous rotation at room temperature.
130
Is a staggered or eclipsed conformer more stable? And why?
Staggered is more stable than eclipsed. The major contributions to the energy difference are stabilizing interactions between the C-H sigma bonding MO on one carbon and the CH antibonding MO on the other carbon: the electrons in the filled bonding MO move partially into the unoccupied antibonding MO. Only in a staggered conformation are the two orbitals parallel, so staggered conformers maximize these stabilizing interactions.
131
What is hyperconjugation?
The delocalization of electrons by the overlap of a sigma orbital with an empty orbital is hyperconjugation. So far just relevant with staggered and eclipsed conformers.
132
What is an anti conformer?
When the dihedral angle between two groups is 180 degrees
133
What is a gauche conformer?
When two adjacent groups have a dihedral angle is between 0 and 120. This type of steric strain is called a gauche interaction.
134
What is steric strain?
The anti and gauche conformers have different energies because of steric strain. Steric strain is the strain experienced by a molecule when atoms or groups are close enough for their electron clouds to repel each other. There is greater steric strain in a gauche conformer because the two substituents are closer together. In general, steric strain in molecules increases as the size of the interacting atoms or groups increases.
135
Explain angle strain in a cycloalkane.
Ideally, an sp3 carbon has bond angles of 109.5 degrees. We can determine the stability of a cycloalkane by determining the difference between this ideal bond angle and the bond angle in the planar cycloalkane. The deviation causes angle strain which decreases cyclopropane's stability.
136
Which is more stable: cyclohexane or cyclopentane?
cyclohexane because it is able to twist and bend out of a planar arrangement to attain a structure that maximizes its stability by minimizing ring strain and the number of eclipsed hydrogens
137
How do you calculate the energy of a cycloalkane?
If we assume cyclohexane is completely free of strain, then we can use the heat of formation (the heat given off when a compound is formed) to calculate strain energy of the other cycloalkanes.
The heat of formation of cyclohexane is -29.5 kcal/mol and divide by 6 to find CH2=-4.92 kcal/mol. The strain in a compound is the difference between its actual heat of formation and its calculated "strainless" heat of formation.
138
What is a chair conformer and what are the angles in one?
The cyclic compounds most commonly found in nature contain six-membered rings because carbon rings of that size can exist in a chair conformer that is almost completely free of strain. A chair conformer is not planar, instead the bond angles are 111 degrees (close to ideal 109.5), and all adjacent bonds are staggered
139
How do you draw a chair conformer?
It's basically a lawn chair.
140
What is a ring flip?
Cyclohexane rapidly interconverts between two stable chair conformers because of the ease of rotation about its C--C bonds. This interconversion is called ring flip. When two chair conformers interconvert, bonds that are equatorial in one chair conformer become axial in the other chair conformer and bonds that are axial become equatorial.
141
What is a boat conformer?
Cyclohexane can also exist as a boat conformer. Like the chair conformer, this boat conformer is free of angle strain. However, it isn't as stable because some of the C--H bonds are eclipsed. The boat conformer is further destabilized by the close proximity of the flagpole hydrogens, and this causes steric strain.
142
Rank the conformers of cyclohexane by stability.
half chair < boat < twist boat < chair
143
What is a half-chair conformer?
When the carbon is pulled down to the point where it is in the same plane as the sides of the boat.
144
What is a twist-boat conformer?
When the carbon is pulled down just a little, it becomes the twist-boat conformer. This is more stable than the boat conformer because the flagpole hydrogens have moved away from each other, thus relieving some steric strain.
145
Are the two chair conformers of a monosubstituted cyclohexane (such as methylcyclohexane) equivalent or no?
not equivalent
146
Why are substituents in an equatorial position more stable than axial in a conformer?
The substituent in the equatorial position has more room and so fewer steric interactions.
147
Explain 1,3-diaxial interactions
Any axial substituent will be relatively close to the axial substituents on the other carbons on the same side of the ring because all three axial bonds are parallel to each other. Because the interacting axial substituents are in 1,3-positions relative to each other, these unfavorable steric interactions are called 1,3-diaxial interactions.
148
What is a cis isomer?
when substituents are on the same side of the ring (up up or down down)
149
What is a trans isomer?
when substituents are on different sides of the ring (up, down)
150
What is a fused ring?
When two cyclohexane rings are fused, one ring can be considered to be a pair of substituents bonded to the other ring. As with any disubstituted cyclohexane, the two substituents can be either cis or trans. The trans isomer has both substituents in the equatorial position. The cis isomer has one substituent in the equatorial position and one in the axial position. Trans-fused rings, therefore, are more stable than cis-fused rings
