CHE 118A Midterm 1

What constitutes a nonpolar bond in terms of electronegativity difference?

less than .5

What constitutes a polar bond in terms of electronegativity difference?

greater than .5 and less than 1.7

When put two electrons in an orbital, what are the two possibilities of interatction?

constructive interference -- waves match up and exaggerate the wave; destructive - waves are out of synch and cancel each other out

What does destructive interference produce in terms of orbitals?

antibonding orbitals -- higher energy orbitals with a node between nuclei

What does sp hybrid orbitals look like?

have large lobe and smaller, are linear

What happens with the unhbridized orbitals?

simply remain there, can interact in pi bonding, as with p orbitals

BH3 is an example of a ____acid because

lewis; it will accept electrons in empty p orbital

Kekule structure...

all explicit, all 90 degrees from one another

How is the structure for condensed alkanes written when there is a substituent attached to a carbon?

C, then H then substituent in alphabetical order

What do parenthesis indicate in condensed formulas?

branches, repeating units, symmetrical ends

pi bonds are (weaker/stronger) than sigma bonds

weaker

Where does a pi bond have a node?

at plane of carbon

chemical thermodynamics

change in energy, what is the extent of a reaction; energetics

chemical kinetics

how fast reaction is taking place; thermodynamic control (governed by change in energy to get a stable product)

kinetic control

rate of reaction is what governs a reaction == the easiest and fastest formed product is the result

arhennius acid

produce H+ in H2O, have H+ in formula

arhennius base

produce OH- in water, have OH- in formula

bronsted-Lowry acid

donate H+; accept H+; water does not have to be involved

Ka =...

-log(H3O+); pH where 50% H+/A-

What is the range of pKas?

-10 to 50 (50 = very weak acid)

A strong acid has a pKa...

less than 0

What makes an acid strong?

size of atom, electronegativity, resonance

Why does size of atom matter in terms of acid strength?

bigger atoms hold onto the H+ poorly; don't bond well with H; poor overlap=weak bond = better dissociation and strong acid

Why does electronegativity matter in terms of acid strength?

more electronegative atoms give stronger acids, more willing to be negative ions; they have a harder time carrying the negative charge

Why does resonance matter in terms of acid strength?

multiple valid structures = spreading out the charge, easier to carry the negative charge

Lewis acid...

accept lone pair into an empty orbital; metal ions (Zn, Fe),

BH3 is an example of a _____

lewis acid

FeCl3 is an example of a ______

lewis acid

lewis base

donate lone pair

BL bases (always/sometimes/never) are lewis bases

always

BL acids (always/sometimes/never) are lewis acids

sometimes

H+ is a ____ acid

lewis

AlCl₃ is a ____ acid

lewis

Do electrophiles/nucleophiles need an empty orbital?

no

electrophile

electron acceptors; generally positive or partial positive or electron deficient; all lewis acids are electrophiles

nucleophile

base to the electrophile acid; donate electrons to electrophiles; anything with extra electrons and can give them is a nucleophile

All BL bases are ______philes

nucleophiles

all lewis bases are ____philes

nucleophiles

CN- acts as a ____phile

nucleophile

Not all electrohphiles are ____ acids

lewis

alkenes

at least one C=C

alkynes

at least one triple bonded C

aromatics

cyclohexane with alternating pi bonds (single, double, single...)

alcohols

have attached OH, NOT HYDROXIDE; polar, will H bond; predominantly acts as an acid

Ether

O bonded between two carbonds C-O-C; don't H bond, not polar

Amines

NH2 or NH or N bonded to three C with lone pair; N acts as a nucleophile

aldehyde

C double bonded to O and single bonded to H; under carbonyl class

Ketone

C double bonded to O; under carbonyl class

carboxylic acid

C double bonded to O and single bonded to OH

ester

C double bonded to O then single bonded to O which is bonded to another C, in middle of chain

amide

C double bonded to O and single bonded to NH2

acyl group

carbon double bonded to O and single bonded to a halogen

nitrile

C triple bonded to N; carboxylic acid derivative, not a carbonyl

does X always mean halogen?

no, can also be another non C/H atom

cycloalkanes are _____saturated

un

What does isobutane look like?

mercedes benz symbol

isopentane...

four carbon chain with methyl group on carbon 2

neopentane...

looks like cross; four carbons all attached to central carbon

as alkanes start getting larger and larger, their shape becomes more and more...

linear

How are the properties of alkanes determined?

by intermolecular forces; only london forces (non polar)

properties of alkanes...

not soluble in water, non polar; low melting and boiling points; high surface area (which leads to high bp due to more contact for temporary dipoles)

for every CH2 added to an alkane, there is a bp addition of...

20-30 degrees

structures with larger surface areas tend to have ___ BP

higher

why is melting point not as affected by surface area?

crystalization -- the compounds don't want to move past one another and become liquid

THough it is hard to melt a spherical structure, it is easy to get it to...

vaporize

if a newman projection is between eclipsed and staggered conformation, it is called...

skewed

the eclipsed newman projection is the ___ state...

transition; high energy so the molecule will not remain like this for long

Why is eclipsed conformation high energy?

intramolecular forces -- torsional strain (eclipsing strain); bonds line up which causes electrons to repel one another

the bigger the mc gets the ____ the eclipsing strain there is

more

gauche conformation

staggerd newman projection where the two larger substituents are adjacent to one another; higher energy than antibonding

homolytic cleavage...

start with A-B -- break into A + B with each getting the same total number of electrons; very rare occurrence (don't like to share); seen in non-polar and gas phase

heterolytic cleavage

A-B -- A+ and B-; uneven electron division; get ions; common insolution, electrophile/nucleophile reaction

better overlap between orbitals =

stronger bonds

How does stability affect radical formation?

the more stable the radical, the easier it is to make; therefore it is easier to make a radical from an unstable bond (more energy favorable to make the radical)

In terms of radical formation in primary, secondary, tertiary, and single carbons, what is the trend?

single carbons have the strongest bond energy, tertiary have the weakest; so therefore it is easier to form a radical from a H bonded to a tertiary carbon; this radical is more stable

hyperconjugation

sp3 neighboring empty p orbitals help stabilize radicals; sp3 orbital will associate with the p orbital and stabilize it, will sort of have resonance

when forming a radical in methane, where does the lone electron frequent in the CH3- formed?

will occupy the empty, unhybridized p orbital because it is lower in energy

Why are tertiary carbonds the easiest to make radicals with?

have 3 sp3 orbitls to help stabilize the radical, so even more stable than primary or secondary

hydrogen (can/cannot) perform hyperconjugation

cannot

radical oxidation

what causes butter/fats/oils to go rancid; radical will oxidize and cause spoilage

radicals can also be used to form...

polymers

forming gasoline...

need 4-12 carbons so it is liquid; natural oil is too long so perform pyrolysis to break up; heat up the chain and it will break up into radicals, can have varying chain lengths; have to let the radicals sit and they will reform new bonds with one naother into smaller shains

Halogenation of alkanes...

add heat or light to form Acid and halogenated alkane, both in gas form

All radical reactions have 3 types of steps...

initiation (formation of radicals: 0 rad ---2 rad, endothermic); propagation (converts 1 radical to another; can be endo or exo; can happen many times); termination (radicals come together, is exothermic

Why are halogens good at halogenation?

they are easy to break

why is it easy to break F-F apart?

both fight over electrons

Out of the halogens, which is the most difficult diatomic molecule to break apart?

Cl-Cl

when F undergoes halogenation, it has a ____ transition state

early; F will not hesistate in gaining the H from the alkane so the transition state is almost nonexistant; transition state is pictured as the two products already formed

When iodine undergoes halogenation, it has a ____ transition state....

late; endothermic reaction; I does not attract the H+ from alkanes as much, the transition state looks largely like the original reactants

Does Iodine undergo radical halogenation?

no, too endothermic

What changes when alkanes undergoing radical halogenation are larger than ethane?

has more than one type of hydrogen, has H bonded to primary and secondary carbons, so halogens can bond to different carbons ratio is different, but expectation is varied from actual nature

What type of carbon does Cl prefer to do radical halogenation with>

secondary over primary, but not really tertiary

What is the selectivity factors for F?

1° = 1; 2° = 1.2, 3° = 1.4

What are the selectivity factors for Cl?

1°=1, 2° = 4, 3° = 5

What are the selectivity factors for Br?

1° = 1, 2° = 80, 3° = 1700

Selectivity of F...

not really selective because the reaction is very exothermic

selectivity of Br

not very interested in reacting, 3° is easiest to form and stableish

very exothermic reaction tend (to be/not to be) selective

not to be

20 carbon chain...

icosane