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CHM 255 Exam 1

Each electron shell contains ______ electrons. 2n^2
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
Describe the shapes of s and p orbitals S-orbital: spherical P-orbital: 2 lobes
Define electronegativity how tightly an atom holds on to its electrons
What is the most electronegative atom and it's value Flourine; 4.0
Electronegativity trend Increase right and up
Differentiate between ionic and covalent bonding Ionic: electron transfer; eneg. diff. > 1.9 (large) Covalent: electron share; eneg. diff. <1.9 (>0.5 = nonpolar)
How can you tell if an atom has a partial negative or positive charge? The more electronegative atom has a partial negative
Know electron configuration; lewis structure
Formal charge formula (Initial # valence electron) - (# nonbonded electron) - (1/2)(# bonded electron)
Define alkane, alkene, and alkyne Alkane: single CH bonded chain Alkene: CH chain with double bond(s) Alkyne: CH chain with triple bond(s)
Alcohol OH (hydroxl) group
Ether single bonded C-O-C
Amine Single bonded N-H on chain
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
Carboxylic acid R-C=O(-OH on C also)
Ester R'-C(=O)-O-R
Amide R"-C(=O)-N-R(R')
Phosphate Ester Central P with =O, 2 O-, and O-R bonded at four sides Holds DNA together
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
Tetrahedron 4 atoms or electron pairs bond angle 109.5
How do unpaired electrons affect bond angles Lead to greater repulsion and change angles
Trigonal Planar 3 atoms or electron pairs bond angle 120
Linear arrangement 2 atoms or electron pairs bond angle 180
An atomic orbital determines _____ % probability to find and electron there 90
Two 1s orbitals form a _____ bond Two 2p orbitals form a _____ bond Sigma; Pi
Hybridization of atomic orbitals Number of electron dense areas... 4=sp3 3=sp2 2=sp
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
Which are hybridized, atoms or bonds? Atoms
Describe resonance The real structure of a molecule (resonance hybrid) is a composite of contributing structures
In arrow pushing, where does the arrow start? The site of the electrons you want to move
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
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
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
Infixes for IUPAC naming Indicates nature of C-C bonds an- all single bonds en- double bond(s) yn- triple bond(s)
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
Intermolecular forces of attraction are known as ____________: caused by temporarily induced dipole moments in atoms and molecules dispersion forces
What causes boiling point to increase? The number of atoms and most branching
What creates a temporary electron dipole? Unsymmetrical electron density
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
Define conformation any 3_d arrangement of atoms that results from rotation around single bonds
The conformations that we care about are the ___________ (least favorable) and ________ (most favorable) highest energy; lowest energy
To draw a _____________ look down the C-C bond and flatten Newman Projection
In the _________ conformation H's are as far apart as possible In the _________ conformation H's are on top of each other staggered; eclipsed
Which has the highest energy, eclipsed or staggered conformation? eclipsed
Eclipsed conformation has ________ _______. Torsional strain
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"
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"
What are constitutional isomers molecules with the same molecular formula but a different arrangement of atoms
* Review substituent chains * (esp. iso, sec, tert)
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.)
When both substituents are in equivalent positions, the one with _____________ gets the lowest number the lower alphabetical ordet
Do you use prefixes when alphabetizing? ONLY iso and neo
For cycloalkanes with one substituent... don't use a number in naming, simply methylcyclo()
How do you number cycloalkanes with 2 or more substituents Number the ring starting with the substituent with the lowest alphabetical order
Why are the hydrogens in O-H more acidic than the hydrogens in C-H3 in acetic acid? Acidity increases with electronegativity!
How can you determine which direction an equilibrium of an acid base reaction wil lie? Lies towards higher pKa
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)
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
Eclipsed CH's lead to ___________ strain; An angle less than _____ leads to angle strain. torsional; 109.5
What do we know about cyclobutane in terms of strain, shapes, and angles? Butterfly shaped; 88 deg. angles; angle strain
What do we know about cyclopentane in terms of strain, shapes, and angles? Envelope shaped; 105 deg. angles
What do we know about cyclohexane in terms of strain, shapes, and angles? Most stable conformation is the CHAIR shape
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
If all CH's are _____________ there is NO torsional strain staggered
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
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
What is steric clashing? When -H H- are facing towards one another
Why are equitorial substituents prefered over axial Axial provide steric interaction; Equitorial is 1.7 kcal/mol more stable
The __________ the substituent the worse the interactions larger
What's the equation to determine free energy difference betqeen equitorial and axial substituents? (Delta G) = -2.3 R T log(Keq)
When there are two substituents they can be on the same side (______) or opposite sides (________). cis; trans
Which is the highest and lowest energy chair conformation - cis or trans? Trans with axial = highest; trans with equitorial = lowest
When attempting to obtain the lowest energy conformation always put the larger group in ___________(axial/equatorial). equitorial
Define delocalization Spreading electron density over a large surface area
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
Bronsted-Lowry acid Proton donor
Bronsted-Lowry base Proton acceptor
Bronsted-Lowry conjugate acid Base accepts a proton (+)
Bronsted-Lowry conjugate base Acid loses a proton (-)
Difference between week and strong acid/base Strong completely donates/accepts H+; weak doesn't completely
How do we measure the strength of an acid? pKa
When deciding if one acid is more acidic than the other you should...? compare the stability of the conjugate bases
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)
What is the inductive effect When there is a nearby group that can pull electronegatively away from the central atom
As electronegativity increases, what happens to the stability of the conjugate base and why Stabilized because it can better accommodate the negative charge
How does acidity change with bond energy down the periodic table and why? Lower BDE = more acidic because of the overlab of the orbitals
How does hybridization affect conjugate base stability sp lower in energy than sp2 or sp3... so more acidic
Created by: jkmccord11



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