Exam 2 Flashcards
1
Q
What do Line/ Skeletal Structures show
A
show connectivity and geometry of hydrocarbons; way to predict physical and chemical properties
2
Q
Degrees of unsaturation
1. cycloalkane
2. alkene
3.alkyne
A
- 1 per ring
- 1 per double bond
- 2 per triple bond
3
Q
Isomer Definition
A
2 compounds with the same molecular formula but different structures (connectivity and geometry) therefore different properties; requires breaking and forming bonds
4
Q
Can Isomers interchange at room temp?
A
No because breaking bonds in required; higher temp -> greater ave energy -> easier to interchange structures.
5
Q
Constitutional/ Structural Isomers
A
compounds with the same molecular formula but different atomic conductivity; ex. butane and
2-methylpropane
6
Q
Functional Groups
A
specific structure that has similar chemical properties whenever it is present in a molecule
7
Q
are alkanes a function group?
A
No because they are very stable and unreactive at room temperature (not special properties)
8
Q
alkene
A
C-C double bond
9
Q
trans isomer
A
r groups are on opposite sides of double bond/ alkene
10
Q
cis isomer
A
r groups are on same side of double bond/ alkene
11
Q
Alkyne
A
C-C triple bond
12
Q
Aromatic/ aryl group
A
hydrocarbon ring alternating double and single bonds
13
Q
Alcohol/ hydroxyl group
A
-OH
14
Q
Ether
A
R-O-R’
15
Q
Aldehyde
A
C double bond O and H bonded to an R group
16
Q
Ketone/ Carbonyl Group
A
C double bond O
17
Q
Carboxylic Acid/ Carboxyl Group
A
C double bond O and -OH bonded to an R group
18
Q
Amine
A
-NH2, -NH or N bonded to 1 or more R groups
19
Q
Amide
A
C double bond O and C-N bonded to a R group
20
Q
Ester
A
C-O and C double bond O bonded to a R group
21
Q
Electronegativity
A
the tendency of an atom in a molecule to attract bonding electron density
22
Q
Electronegativity Trend
A
Increases across period and decreases down group.
23
Q
Most electronegative element
A
Fluorine; 4.0
24
Q
Valence Bond Theory
A
a quantum mechanical model for bonding from overlap of AO; AO’s combine/ change shapes to optimise energy
25
hybrid orbital
combination of valence atomic orbitals that emphasize concentration of electron density in specific directions; due to greater AO overlap when forming sigma bonds
26
In phase hybrid orbital
?
27
out of phase hybrid orbital
?
28
sp hybridization
combining valence s AO with valence p AO; 1:1 ratio of s and p characteristics and energetics
29
sp2 hybridization
1 valence s AO and 2 valence p AO; more p orbital characteristics and closer to p orbitals energy level
30
sp3 hybridization
1 valence s AO and 3 valence p AO; even more p orbital characteristics and even closer to p orbitals energy level
31
Sigma Bond Formation
when 2 hybridized orbitals, each with 1 unpaired electron, overlap
32
Pi Bond Formation
overlap of unhybridized orbitals
33
Why Hybridize?
bonds formed from overlapping decrease energy (more stable)
34
sp hybridized geometry
linear
35
sp2 hybridized geometry
trigonal planar (bent)
36
sp3 hybridized geometry
tetrahedron (trigonal pyramidal)
37
Wedge dash notation
straight lines: in plane of page
dashed wedges: going away/behind the page
solid wedges: coming out of the page
38
sp hybridized bond angle
180 degrees
39
sp2 hybridized bond angle
120 degrees
40
sp3 hybridized bond angle
109.5 degrees
41
Bent's Rule
a hybrid orbital on a central atom has a greater p character and greater and electronegativity than the other atoms forming the bond
42
N hyb
N hyb= number of sigma bonds (+ 1 if any lone pairs present)
N hyb=2= sp
N hyb=3=sp2
N hyb=4= sp3
43
Resonance Structures
weighted average of a set of lewis structures to represent a molecules true electron density distribution; simultaneous blend of lewis structures with delocalized electrons
44
Why do resonance structures exist?
because not every bond is strictly between 2 atoms/ not localized
45
What does not change between lewis structures in a resonance structure?
connectivity, hybridization, geometry
46
Resonance Structure hybridization
hybridization must accommodate all resonance structures (go with the lowest hybridization)
47
How to know the dominant contributor of the structure
Formal Charge; most optimal formal charge -> most prominent electron distribution
48
Resonance Hybrid
all resonance structures of a molecule separated each from the next by a double-headed arrow.
49
Conformations/ Conformers
structures that differ only because of rotation around a sigma bond; no need to break bonds to get from one structure to another; same IUPAC names
50
How much energy is required for a molecule to rotate around and sigma bond and why?
low energy because sigma bond is cylindrically symmetrical when rotating around internuclear axis
51
What causes any variation in rotation around sigma bond energy?
certain degrees of rotation have more electron repulsion because electrons closer together.
52
Enantiomers/ Optical Isomers
Molecules that are non superimposable mirror images of each other (like right and left hands)
53
Enantiomers/ Optical Isomers Ex
the drug thalidomide; given to pregnant woman but one enantiomer caused birth defects
54
Chiral Center
asymmetric carbon bonded to 4 different groups
55
Intermolecular Forces
attractive forces between molecules
56
Types of Intermolecular Forces
London Dispersion Forces (LDF), Dipole-Dipole Attractions
57
What influences Intermolecular Force strength?
geometry influences LDF strength BECAUSE influences how different electron densities overlap; more overlap= stronger forces
58
Viscosity
measure of liquids resistance to flow; stronger LDF's, higher the viscosity
59
Structural Isomers
same molecular formula, different connectivity
60
Geometric Isomer
cis/trans or E/Z isomers; type of stereoisomerism that describes certain arrangement of atoms within molecules.
61
Bond Polarity
the distribution of electric charge across a chemical bond between two atoms.
62
Polar Bond
unequal sharing of electron density
-large electronegativity difference: very polar
-small electronegativity difference: less polar
63
Non Polar Bond
electronegativity difference of zero or very close to zero; close to equal sharing of electron density
64
Dipole Moment
unequal distribution of electron density between bonded atoms in a molecule
65
Strength of LDFs
Increased strength:
-more electrons
-more polarizable electron cloud (more squishy)
-packing density/ larger surface area (long chain saturated molecule higher LDFs than branched or compacted unsaturated molecule)
66
Strength of IMFs
-weaker than covalent bonds (except in polymers)
-strength reflected by phase change temperature, viscosity, surface tension, etc
67
Dipole-Dipole Interactions
attraction between molecules with a permanent dipole (as opposed to LDF temporary dipoles)
68
Dipole-Dipole Interactions Requirements
-polar bonds (strength/magnitude of polar bond impacts strength of dipole; ex. C-H bond not very polar so dipole is small/weaker)
-molecular asymmetry (symmetry-> dipoles cancel out and molecule is nonpolar)
69
Hydrogen Bonding Requirements
1) hydrogen bonded to a O,F, or N
2)lone pair of electrons on a higher electronegative/ electron rich atom (F,O,N)
70
Hydrogen Bonding
strongest case of dipole dipole forces formed between H and FON atoms to produce partial pos and neg charges
71
polymer
large molecules made by covalently linking many smaller molecules (monomers)
72
addition polymers
polymers made by addition reactions (ex. alkene-> saturates to form an alkane); initiated by free radical
ex. ethylene -> polyethylene
73
properties of polymers
many slightly different length chains bonded together so a variety of different melting points
ex. why plastic loses shape/ deforms before fully melting
74
IMF of polymers
the larger the IMF's the stronger and more ridged the structure is (cant move past each other as easy)
75
Do linear or branched polymers have stronger IMF's?
Linear because they can be backed close together; smaller r so greater attraction
76
cross linking
covalent sigma bonds between 2 seperate polymer strands (not at either end of strand)
77
Diene Polymers
-alkene polymers with a double-single-double bond pattern
-monomer: look for 4 carbon long structure.
78
what does cross linking to do strength of polymer?
gives a material a more rigid structure/limits movement and potentially a better-defined shape; stronger IMF's
79
Diene Polymers mechanism
-formed by addition reactions initiated by reactive free radical
-resulting polymer can still react because it has an alkene functional group in it
80
Vulcanization
process that hardens/ toughens rubber, makes it more resistant to temperature changes and more elastic **due to sulfur cross linking**
81
Copolymer properties
distinctive unique properties; differs from properties of mixture of individual monomer strands unbonded
82
Copolymers
polymers made by polymerizing a mixture of 2 or more different monomers
83
Condensation Reaction
new bond formed and smaller molecule kicked out (normally water)
ex. carboxylic acid and alcohol -> ester and water (OH from carboxylic acid and H from alcohol form water and C-O bond forms)
84
Condensation polymer
polymer formed via condensation rxn; forms amide or ester linkages
85
2 types of condensation polymer
polyester and polyamide
86
Polyamide
polymer in which individual units are held together by amide linkages; amide group on one side and carboxylic acid group on other
87
Polyamide IMF
very strong LDF, dipole dipole attraction (aligned amine groups with neighboring strands), hydrogen bonding
88
Polyamide ex
-nylon66
-kevlar
-proteins and peptides (biopolymers)
89
Polyester
polymer in which individual units held together by ester linkages as result of condensation rxn
90
Polyester IMF
ester function group is polar
-> increases IMF; LDF, dipole dipole, and, hydrogen bonding
91
Viscosity of Polymers
?
92
Why are Carboxylic Acid Hydrogen bonds stronger than Alcohol H bonds?
Because of their acidic properties (donating a H+); reaction yields a more stable product while same reaction (H+ donation) of alcohol produces less stable product (explains reactivity differences)
93
What influences strength of LDFs in Polymers?
-chain length: longer chain, more LDF's
-packing density: closer together, larger the LDF's-> harder, denser, more rigid structures.
94
How do modifications of side chains impact properties?
can change strength based on change in LDF present and could change reactivity
95
Polypeptides
naturally occuring polyamides; amino acids held together by amide bonds (peptide bonds)
96
what kind of amino acids are the 20 amino acids (R groups) that react in our body
alpha amino acids
97
What does the R groups in polypeptide structure impact?
3D structure of the protien
98
Primary Structure
amino acid sequence; linked by amide bonds/ peptide bonds
99
Secondary Structure
interactions between different parts of backbone
-2 most common structures : alpha helix and beta pleated sheet
-R groups stick out of secondary structure; determine properties ex polarity
100
Tertiary Structure
formed by interaction of R side groups; non covalent molecule interactions (IMF between protein and other molecules)
101
Quaternary Structure
multiple protein strands sticking together
102
DNA
2 polymer strands that coil around each other to form double helix
-monomer units : nucleotides
103
Nucleobases; complementary base pairs
nucleobases are the side groups the H bond together between the sugar (deoxyribose) backbone of the DNA
-A and T; G and C; equal quantities of base pairs
104
Glycerolipids
class of lipids composed of glycerol and fatty acids; 3 fatty acid and 1 glycerol (CH2OH-CHOH-CH2OH)
105
fatty acid
long, unbranched hydrocarbon chain with carboxylic acid on end
106
saturated vs unsaturated fatty acid and melting point
saturated: only single C-C bonds; solid at room temp (fat/wax)
unsaturated: includes alkene(s) C=C; liquid at room temp (oil)
