Test 1 Flashcards
What is the electronegativity difference of an ionic bond?
Greater than 1.9
What is the electronegativity difference of a polar covalent bond?
0.5-1.9
What is the electronegativity difference of a nonpolar covalent bond?
Less than 0.5
How do you determine formal charge?
Valence electrons on periodic table minus # of bonds and lone electrons in molecule
How do the melting points and boiling points of ionic substances compare to covalent substances?
Ionic substances have high melting and boiling points
what determines a molecular substances physical properties?
types and strengths of intermolecular forces
what are three types of intermolecular forces?
dispersion forces
dipole-dipole forces
hydrogen bonding forces
what is a protic solvent?
a solvent that donates a hydrogen bond
what is an aprotic solvent?
a solvent that cannot serve as a hydrogen-bond donor
what is a polar solvent?
a solvent with a dielectric constant of 15 or greater
what is a nonpolar solvent?
a solvent with a dielectric constant less than 15
what is a dielectric constant?
a measure of a solvent’s ability to insulate opposite charges from one another
what two factors determine if a substance is a good solvent?
- separate solute particles (same type and strength of intermolecular forces)
- keep them separated (if ionic or polar molecules make up solute, requires a large dielectric constant)
what is a bronsted-lowry acid
substance that donates a proton
what is a bronsted-lowry base?
accepts a proton
what is needs to be stable for a substance to be an acid?
anion (conjugate base)
what 5 factors stabilize the anion of an acid?
- more electronegative
- larger radius
- delocalization with resonance
- delocalization through electron withdrawing
- more s character (% of hybrid orbital that s constitutes)
what is the inductive effect?
the polarization of the electron density of a covalent bond by the electronegativity of a nearby atom
define the acid dissociation constant
K = [A-][H3O+]/HA
How do you calculate PKeq?
pKha - PKbh+
acid minus conjugate acid, according to equation given
what must be true about PKeq for a reaction to be favorable?
it must be negative
what is the general formula for an alkane?
CnH2n+2
what are constitutional isomers?
compounds with the same molecular formula but a different connectivity of their atoms
What is a bicycloalkane?
an alkane containing two rings that share two carbons
how do you name a bicycloalkane
bycyclo[# of nonshared carbons in big ring. # of nonshared carbons in small ring. # of bridge carbons]suffix of total carbons-ane
what is a conformation
an arrangement of atoms that results from rotation about a single bond
what is strain?
instability within a structure that results in a higher internal energy
what is a staggered conformation?
a conformation where atoms are as far apart as they can be
what is torsional strain?
strain associated with not being in the minimum energy staggered conformation
what is an anti conformation
largest groups are 180 degrees apart
what is a gauche conformation?
groups on carbon atom are 60 degrees apart
what is angular strain?
any deviation from the hybrid atomic orbital’s normal angles
what is steric strain?
any structural conformation where nonbonded atoms or groups are closer than the sum of their radii
What is the predicted angle for sp hybridization?
180 degrees
what is the predicted angle for sp2 hybridization?
120 degrees
what is the predicted angle for sp3 hybridization?
109 degrees
what is an eclipsed conformation?
a conformation when the groups on one carbon are as close as possible to the groups on adjacent carbon
what is a dihedral angle
the angle between two planes that intersect carbon and a carbon-attached group.
what is energy a function of in a torsional energy diagram
dihedral angle
how does isopropyl alkyl group relate to isobutyl and isopentyl alkyl groups?
the CH(CH3)2 isopropyl group is attached to CH2 in isobutyl and a (CH2)2 group in isopentyl
what are the common names of three carbon alkyl groups
- propyl
2. isopropyl
what are the names of four carbon alkyl groups
- n-butyl
- sec-butyl
- tert-butyl
- isobutyl
How does branching in constitutional isomers affect melting/boiling points?
branching decreases surface area which decreases dispersion forces and therefore melting/boiling points
how does branching of constitutional isomers effect heat of combustion?
branching increases stability so it decreases heat of combustion
what is heat of combustion?
heat released when one mole of a substance in its standard state is burned; associated with internal energy
what is the primary strain in cyclopropane?
angular strain from compressing 109.5 degree bond angles to 60 degrees
what is small ring strain?
a strain associated with ring sizes below 6 carbons arising from non-optimal bond angles
why does cyclopropane have high torsional strain?
it is planar so it has 6 pairs of eclipsed C-H bonds
2 ways rotating C-C bonds in a cycloalkane affects strain energy
- decreases torsional strain from eclipsed interactions
2. increases angular strain
why is chair conformation of cyclohexane so favorable?
minimal angular strain and all C-C bonds are staggered
why is twist-boat cyclohexane favorable to boat?
the twist relieves the torsional strain from the four pairs of eclipsed C-H interactions and the steric strain from “flag pole” hydrogens
what is a 1,3 axial (diaxial) interaction?
steric strain arising from an axial substituent with another axial group on the same side of the ring
why is envelope conformation favorable to planar cyclopentane?
bending a carbon out of the plane relieves torsional strain from 10 pairs of eclipsed C-H, even though angular strain is added by reducing angle from 108 to 105
how does the size of a substitute group effect the conformation of cyclohexane?
the bigger the group, the more it will favor equatorial position
what happens when large substitute groups like tert-butyl can’t avoid being in axial position?
most abundant conformation will be twist-boat
what are substitution placements for cis 1,2 cyclohexane?
equatorial AND axial
what are the substitution placements of trans 1, 2 cyclohexane?
diaxial OR diequatorial
what are the substitution placements of cis 1,3 cyclohexane?
diaxial OR diequatorial
what are the substitution placements of trans 1,3 cyclohexane
equatorial AND axial
what are the substitution placements of cis 1,4 cyclohexane
equatorial AND axial
what are the substitution placements of trans 1,4 cyclohexane
diaxial OR diequatorial
what are four factors affecting reaction rate?
- collision frequency
- proper orientation
- availability of sufficient energy
- temperature
Why is fluorine not used in halogenation reaction?
reacts too quickly and violently
why is iodine not used in halogenation reactions?
its activation energy is too high
why does Br selectively halogenate tertiary carbons and chlorine doesn’t?
it has a large activation energy, by Hammond’s postulate the transition state looks like product and therefore has considerable free radical character. the free radical character is stabilized by hyperconjugation. chlorine transition state doesn’t have as much free radical character
why is Cl more reactive than Br in halogenation?
Cl has a lower activation energy for rate determining step
what is the change in enthalpy?
difference in energy between products and reactants in a reaction
what is a transition state
higher energy point on a reaction path diagram
what is an activated complex
chemical structure during transition state
what is activation energy
difference in energy between transition state and reactants
what is the chain initiation of halogenation
formation of radical halogen from nonradicals
what is chain propagation of halogenation
reaction of radical intermediate and a molecule to give new radical intermediate and new molecule
what is chain termination in halogenation?
radical couplings and disproportionation
what is disproportionation
hydrogen is transferred from one radical to a radical of same species, making an alkane and the molecule that lost hydrogen uses the electron from its radical and the electron from hydrogen to form an alkene
