CHM 255 Exam 1
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| Each electron shell contains ______ electrons. | 2n^2
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| What are the 3 rules for filling orbitals | 1. Fill lower electron energy orbitals 1st
2. No more than 2 electrons/ orbital
3. Fill all orbitals with same energy with 1 electron before putting into 2nd
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| Describe the shapes of s and p orbitals | S-orbital: spherical
P-orbital: 2 lobes
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| Define electronegativity | how tightly an atom holds on to its electrons
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| What is the most electronegative atom and it's value | Flourine; 4.0
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| Electronegativity trend | Increase right and up
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| Differentiate between ionic and covalent bonding | Ionic: electron transfer; eneg. diff. > 1.9 (large)
Covalent: electron share; eneg. diff. <1.9 (>0.5 = nonpolar)
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| How can you tell if an atom has a partial negative or positive charge? | The more electronegative atom has a partial negative
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| Know electron configuration; lewis structure |
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| Formal charge formula | (Initial # valence electron) - (# nonbonded electron) - (1/2)(# bonded electron)
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| * FORMAL CHARGE CHART * |
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| Define alkane, alkene, and alkyne | Alkane: single CH bonded chain
Alkene: CH chain with double bond(s)
Alkyne: CH chain with triple bond(s)
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| Alcohol | OH (hydroxl) group
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| Ether | single bonded C-O-C
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| Amine | Single bonded N-H on chain
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| Aldehyde vs. Ketone | Aldehyde: R-C=O(-H off C also) at the END
Ketone: R-C=O(R' off C also) in the middle
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| Carboxylic acid | R-C=O(-OH on C also)
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| Ester | R'-C(=O)-O-R
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| Amide | R"-C(=O)-N-R(R')
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| Phosphate Ester | Central P with =O, 2 O-, and O-R bonded at four sides
Holds DNA together
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| What are bond angles and the shape of molecules dictated by? | A desire to keep the valence shell electrons as far away from one another as possible
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| Tetrahedron | 4 atoms or electron pairs
bond angle 109.5
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| How do unpaired electrons affect bond angles | Lead to greater repulsion and change angles
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| Trigonal Planar | 3 atoms or electron pairs
bond angle 120
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| Linear arrangement | 2 atoms or electron pairs
bond angle 180
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| An atomic orbital determines _____ % probability to find and electron there | 90
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| Two 1s orbitals form a _____ bond Two 2p orbitals form a _____ bond | Sigma;
Pi
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| Hybridization of atomic orbitals | Number of electron dense areas...
4=sp3
3=sp2
2=sp
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| How many sigma & pi bonds? a. sp3 b. sp2 c. sp | a. 4 sp3 --> 4 sigma
b. 3 sp2 + 1 p ---> 3 sigma; 1 pi
c. 2 sp + 2 p ---> 2 sigma; 2 pi
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| Which are hybridized, atoms or bonds? | Atoms
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| Describe resonance | The real structure of a molecule (resonance hybrid) is a composite of contributing structures
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| In arrow pushing, where does the arrow start? | The site of the electrons you want to move
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| Preference in resonance structures given by what 4 things? | 1. Atoms with completed octets
2. Maximum # covalent bonds
3. Least separation of unlike charges
4. Negative charge on more electronegative atom
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| Electronegativity: C, H, N, O, F, Cl, Br | C: 2.5; H: 2.1; N: 3.0; O: 3.5; F: 4.0; Cl: 3.0; Br: 2.8
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| Prefixes for 1-10 Carbons | 1-meth; 2-eth; 3-prop; 4-but; 5-pent; 6-hex; 7-hept; 8-oct; 9-non; 10-dec
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| Infixes for IUPAC naming | Indicates nature of C-C bonds
an- all single bonds
en- double bond(s)
yn- triple bond(s)
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| Suffix for each functional group in IUPAC (hydrocarbon, alcohol, aldehyde, ketone, carboxylic acid) | e-hydrocarbon; ol-alcohol; al-aldehyde; one-ketone; oic acid-carboxylic acid
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| Intermolecular forces of attraction are known as ____________: caused by temporarily induced dipole moments in atoms and molecules | dispersion forces
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| What causes boiling point to increase? | The number of atoms and most branching
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| What creates a temporary electron dipole? | Unsymmetrical electron density
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| The boiling point of a compound is ___________. ________ is needed to overcome attractive forces that occur in the liquid state. | The temperature at which liquid molecules are converted into gas; Energy
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| Define conformation | any 3_d arrangement of atoms that results from rotation around single bonds
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| The conformations that we care about are the ___________ (least favorable) and ________ (most favorable) | highest energy; lowest energy
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| To draw a _____________ look down the C-C bond and flatten | Newman Projection
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| In the _________ conformation H's are as far apart as possible In the _________ conformation H's are on top of each other | staggered; eclipsed
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| Which has the highest energy, eclipsed or staggered conformation? | eclipsed
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| Eclipsed conformation has ________ _______. | Torsional strain
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| What are the different types of staggered conformation and their relative energies | Lowest energy has CH3 groups farthest apart: "anti"
Other ways to arrange staggerd are ~0.9kcal/mol higher in energy: "gauche"
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| What are the different types of eclipsed conformation and their relative energies | 2 conformations with CH3 groups not as close as possible ~ 3.5 kcal/mol higher than "anti"
Highest energy structure has both CH3 groups eclipsed and is ~5kcal/mol higher energy than "anti"
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| What are constitutional isomers | molecules with the same molecular formula but a different arrangement of atoms
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| * Review substituent chains * (esp. iso, sec, tert) |
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| What do you do when there are two or more of the same substituents | 1. Number where the substituents are on the chain
2. Use prefix before substituent name (i.e. di, tri, etc.)
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| When both substituents are in equivalent positions, the one with _____________ gets the lowest number | the lower alphabetical ordet
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| Do you use prefixes when alphabetizing? | ONLY iso and neo
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| For cycloalkanes with one substituent... | don't use a number in naming, simply methylcyclo()
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| How do you number cycloalkanes with 2 or more substituents | Number the ring starting with the substituent with the lowest alphabetical order
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| Why are the hydrogens in O-H more acidic than the hydrogens in C-H3 in acetic acid? | Acidity increases with electronegativity!
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| How can you determine which direction an equilibrium of an acid base reaction wil lie? | Lies towards higher pKa
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| What's the trick for determining if you've numbered correctly in a multiple choice? | Want the number of substituents to add to the lowest possible number (i.e, 4,5,5 > 3,4,4)
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| What do we know about cyclopropane in terms of strain, shapes, and angles? | Carbons are planar with 60 deg. angles' lots of angle and torsional strain
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| Eclipsed CH's lead to ___________ strain; An angle less than _____ leads to angle strain. | torsional; 109.5
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| What do we know about cyclobutane in terms of strain, shapes, and angles? | Butterfly shaped; 88 deg. angles; angle strain
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| What do we know about cyclopentane in terms of strain, shapes, and angles? | Envelope shaped; 105 deg. angles
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| What do we know about cyclohexane in terms of strain, shapes, and angles? | Most stable conformation is the CHAIR shape
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| What's the difference between axial and equatorial? | Ax: up and down on alternating carbons
Eq: slanted on angles in the opposite direction of the axials
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| If all CH's are _____________ there is NO torsional strain | staggered
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| What's the highest energy conformation for a cyclohexane & 3 characteristics? | Boat (both ends point in same direction)
Steric clashing; torsional strain; 6.5 kcal/mol higher energy than chair
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| What is the twist boat conformation? | A twists of the boat to relieve strain and sterics that i s1kcal/mol lower in energy than the boat conformation
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| What is steric clashing? | When -H H- are facing towards one another
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| Why are equitorial substituents prefered over axial | Axial provide steric interaction; Equitorial is 1.7 kcal/mol more stable
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| The __________ the substituent the worse the interactions | larger
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| What's the equation to determine free energy difference betqeen equitorial and axial substituents? | (Delta G) = -2.3 R T log(Keq)
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| When there are two substituents they can be on the same side (______) or opposite sides (________). | cis; trans
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| Which is the highest and lowest energy chair conformation - cis or trans? | Trans with axial = highest; trans with equitorial = lowest
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| When attempting to obtain the lowest energy conformation always put the larger group in ___________(axial/equatorial). | equitorial
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| Define delocalization | Spreading electron density over a large surface area
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| How do you determine which resonance structure would contribute the most to the hybrid (3) | WANT:
1. More covalent bonds
2. Least # lone pairs
3. Saturated carbons
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| Bronsted-Lowry acid | Proton donor
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| Bronsted-Lowry base | Proton acceptor
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| Bronsted-Lowry conjugate acid | Base accepts a proton (+)
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| Bronsted-Lowry conjugate base | Acid loses a proton (-)
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| Difference between week and strong acid/base | Strong completely donates/accepts H+; weak doesn't completely
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| How do we measure the strength of an acid? | pKa
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| When deciding if one acid is more acidic than the other you should...? | compare the stability of the conjugate bases
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| What determines conjugate base stabilization (4) | 1. Inductive effect
2. Resonance
3. Electronegativity of the atom with the anion (across)
4. Hybridization of the atom the anion resides on
5. Bond dissociation energy (down)
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| What is the inductive effect | When there is a nearby group that can pull electronegatively away from the central atom
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| As electronegativity increases, what happens to the stability of the conjugate base and why | Stabilized because it can better accommodate the negative charge
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| How does acidity change with bond energy down the periodic table and why? | Lower BDE = more acidic because of the overlab of the orbitals
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| How does hybridization affect conjugate base stability | sp lower in energy than sp2 or sp3... so more acidic
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