orgo Flashcards
Which is stronger, sigma or pi bonds?
sigma bonds; allow for electron density to be concentrated to a much larger degree between the two nuclei.
What are characteristics of pi bonds?
- no rotation
- weaker
- less stable
- more reactive
what are characteristics of sigma bonds?
- allow rotation
- stronger
- more stable
- less reactive
What is definition of hybridization?
Atoms, when bonded, hybridize/ mix their higher and lower energy valence electron orbitals to form “hybrid orbitals” with intermediate energy.
How do you determine the hybridization?
count # of sigma bonds and add # of pairs of unbounded electrons = superscript
What is the theory that predicts which space molecules will take due to the repulsion of lone pairs of electrons.
VSEPR- Valence Shell electron Pair Repulsion Theory
What is sp hybridization and angle?
Linear[180 ̊]
what is sp^2 hybridization and angle?
TrigonalPlanarorBent[120 ̊]
What is sp^3 and angle?
Tetrahedral, Trigonal Pyramidal, or Bent [109.5 ̊]
what is sp^3d hybridization and angle?
TrigonalBipyramidal,Seesaw,T-Shaped,orLinear[90 ̊/120 ̊or 180 ̊]
what is sp^3d^2 hybridization and angle?
Octahedral, Square Pyramidal, or Square Planar [90 ̊]
Q4. Rank the following according to decreasing bond length: a) triple bonds, b) double bonds, c) single bonds.
single > double > triple
Rank the bonds listed above according to increasing stability.
a) triple bonds, b) double bonds, c) single bonds.
stability= thermodynamic stability
triple bonds are harder to break= more stable
double
single
Rank the bonds listed above according to increasing reactivity:
a) triple bonds, b) double bonds, c) single bonds.
alkene (double) > alkynes (triple) > alkane (single)
Rank the bonds listed above according to increasing bond strength. a) triple bonds, b) double bonds, c) single bonds.
triple > double > single
what atom has the smallest electronegativity?
francium = .7
what atom has the largest electronegativity?
Fluorine = 4
Energy is always ____ when a bond is formed, and ____ when a bond is broken
released; required
what are the exception to the octet rule?
- hydrogen and helium- stable with only two electrons in their valence shells H2
- boron and beryllium; stable with only six electrons in their valence shells BF3
- atoms from the THIRD period or higher can accept more than 8 electrons (PCl5, SF6, PO4 3-, SO4 2-
The ___ stable the bond, the ___ will be the heat of combustion.
less; greater
The __ stable the bond, the __ the heat of combustion
more;lower
What is coordinate covalent bond?
bond in which both electrons shared in the bond are donated by ONE atom- Lewis base is donor molecule and Lewis acid is recipient.
What is coordinate covalent bond?
bond in which both electrons shared in the bond are donated by ONE atom- Lewis base is donor molecule and Lewis acid is recipient.
If there’s no lone pair then there’s no
what is equation of formal charge?
FC= valence - assigned.
Do resonance structures resonate back and forth between forms?
No it’s permanent
what is the most stable resonance structure?
the one with the most resonance structure, the one with negative charge on the most electronegative atom, the one with least formal charge and with atoms that have full octet.
what are aromatic compounds?
conjugated unsaturated ring system that exhibit greater stability than one would expect based on either resonance, conjugation alone. benzene i has greater stability than unsaturated compounds with two/ three double bonds
What’s Huckels rule on aromaticity?
a ring system must have 4n + 2pi elections
How can you predict the number of optically active stereoisomers for any compounds?
2^n where n= number of chiral centers
what is a chiral center?
usually contain at least one carbon atom with four nonidentical substituents
What are conformational isomers?
- same exact molecule but bonds are rotated bonds, … gauche, eclipse, staggered conformation on energy diagram)
- NOT TRUE ISOMERS
what are structural isomers?
- same formula but with different connectivity
ex: 2-methylpentane and 3methylpentane are both C6H14
what are stereoisomers?
same formula, same connectivity but different in the 3D arrangement of their substituents.
- enantiomers and diastereomers.
what are enantiomers?
non identical and non superimposable mirror images- at least ONE chiral center.
can enantiomers rotate plane polarized light? which direction?
Yes enantiomers rotate plane polarized light.
R and S enantiomers can rotate light in either clockwise or counterclockwise direction.
clockwise= + = d dextrorotary
counterclockwie= - = levorotary
Is R configuration clockwise or counterclockwise? what about S?
R= clockwise S= counterclockwise
what is the difference between optically active and inactive ?
To be optically active means that a substance does rotate plane- polarized light. Optically inactive compounds do not rotate plane-polarized light.
Enantiomers have the same physical properties such as boiling point, reactivity, EXCEPT for … (2) ?
- how they rotate plane polarized light
- products they form when reacted with another chiral compound.
What are diastereomers?
Two molecules with the same formula and the same bond-to-bond connectivity that are non identical but are NOT mirror images.
- geometric isomers
- epimers
- anomers
An unknown molecule has an absolute configuration of S and rotates plane-polarized light 15 degrees in the clockwise direction. Which of the following molecules is enantiomeric to the unknown?
A) Absolute configuration is R; rotates plane-polarized light 15°; levorotary
B) Absolute configuration is R; rotates plane-polarized light 165°; levorotary
C) Absolute configuration is S; rotates plane-polarized light 15°; dextrorotary
D) Absolute configuration is R; rotates plane-polarized light 15°; dextrorotary
a
what are geometric isomers?
each of two or more compounds that differ from each other in the arrangement of groups with respect to a double bond, ring, or other rigid structure.
what is the difference between E1/sn1 and E2/SN2?
E1/SN1 form carbocation and are in 2 steps: carbocation formation (slow step) + attack of carbonation (fast step)
+ better on weak bases, polar protic solvents and tertiary carbons + anything with bad leaving group.
sn1 forms racemic mixture
E2/Sn2- quick and for good nucleophiles, methyl, 1 or 2 carbons and strong/bulky BASES
what are mp/ bp of alkanes?
1) bp and mp increases with with increasing chain length and/ or molecular weight.
2) bp decreases with increasing branching
3) straight chain alkanes have the highest melting points.
4) Among branched alkanes, increased branching INCREASES melting point.
What causes ring strain?
- axial/ equatorial have large substituents too close
Are alkane soluble in water? what is their characteristic density, polarity? stop form?
most alkanes are oils or gases, therefore they are insoluble in water and have very low density and are non polar.
Is the heat of combustion of alkanes more or less stable as you add more -CH2 groups?
rank: cyclopropane, cyclobutane, cyclohexane, cycooctane according to increasing heat of combustion.
more stable = lesser heat of combustion
more ring strain = less stable= more heat of combustion
therefore from least to highest heat of combustion:
cyclohexane, cyclooctane, cyclobutane, cyclopropane.
which compounds has the most ring strain, cyclohexane or cycle butane?
cyclohexane or cyclononane?
- cyclobutane
- cyclononane
How do you synthesize an alkane from an alkene? (double to single)
Reduce an alkene with H2, in the presence of a metal catalyst.
If new bonds are formed on the same side it’s san addition and if new bonds are formed on different sides it’s anti addition.
What are 3 notable alkene characteristics?
1) Alkenes are good nucleophiles because of the pi electron that can attack electrophiles.
2) alkenes are weakly electron withdrawing when located near (one carbon away) from another atom.
3) alkene’s stability increases with R group (alkyl substituents); so tetrasubstituted > trisubstituted > disubstituted> mono substituted > unsubstituted
what is a nucleophile?
donates an electron pair to an electrophile to form bond with that electrophile ( lewis base)
what is an electrophile?
positively charged or neutral species having vacant orbitals that are attracted to an electron rich centre and will receives electron pair from nucleophile and kicks off leaving group.
what is –Ph, such as Phenyl?
a benzene attached to a primary structure; benzene attached to -CH2
what is –Ar, such as aryl?
a benzene attached to another aromatic ring
what is C6H5?
benzene- unsaturated
when you have double bonds, such as in C6H5, is the structure saturated or unsaturated?
unsaturated.
double bonds keep fluidity
What are the boiling and melting point characteristics of alcohols? In relation to hydrocarbon?
1) BP and MP goes up with molecular weight
2) BP and MP goes down with increased branching
3) MP goes up with increasing polarity and Hydrogen bonding.
MUCH HIGHER BOILING AND MELTING POINTS THAN HYDROCARBONS
why are alcohols soluble in water?
they can form hydrogen bonding and therefore have strong solvent/solute attraction
What are the three element have can be hydrogen bond donor/ acceptor?
F,O,N
Through what mechanism can you form an alkyl halide from an alcohol?
SN2 and SN1
in both, OH is a nucleophile, BUT
-in SN2 the halide is attacked by the OH and the resulting halide ion kicks off H2O leaving group and replaces it.
- in SN1, water dissociates by itself (slow rate limiting step) and forms a carbocation that the halide ion can then attack
Can you further oxidize primary, secondary and tertiary alcohols? what would you get?
1 ̊ Alcohols–> Aldehyde—> CarboxylicAcids
2 ̊Alcohols–>Ketones
3 ̊ Alcohols cannot be further oxidized
What re common oxidizing agents?
O3, Cr2O7, CrO4, KMnO4, Jones, Collins, PCC, PDC
Potassium dichromate is often used as an oxidizing agent. A solution of dichromate ions (Cr2O72-) is orange, but a solution of chromium ions (Cr3+) is green. If alcohol A is reacted with potassium dichromate and produces a green solution, and alcohol B is reacted with the same reagent and produces an orange solution, what can be inferred about the two alcohols, A and B?
B is unreacted because it forms dichromate ions and that owed mean it did not oxidize.
Green solution means the reactant was oxidized
What are reduction reagents? are there specific reduction reagents for specific compounds?
NaBH4- aldehydes and ketones because’s its’ weaker – on has ONE H- equivalent
LiAlH4 and H2/ pressure for aldehydes, ketones, carboxylic acids and esters –> strong because it has 2 H equivalent
What is the Pinacol rearrangement (polyhydroxyl alcohols)
vicinal- diol + hot acid –> ketone or aldehyde
What reagents do you use to protect alcohol groups in reactions?
TMS will put a Si(Ch3)3 cap.
MOM will put a MOM cap on it.
What happens if you react an alcohol with a SOCl2? PBr3?
ROH + SOCl2 –> RCl
ROH + PBr3 –>RBr
How do you form Tosylates/ Mesylates?
Tosyl-Cl + ROH Tosyl-OR + HCl
o STEPS:
1) The alcohol attacks the tosyl or mesyl halide via SN2, kicking off a halide ion.
2) A hydrogen is abstracted by the halide ion, quenching the charge on the oxygen.
How do you remove protecting group from an OH?
acidification to remove protecting group or restore alcohol.
How do you go from an alcohol to an alkene? using what reagent and steps?
dehydrate the alcohol
1) The alcohol is protonated by the acid
2) The “good leaving group water” leaves, forming a carbocation
3) Methyl or hydride shifts can occur, but only if it results in a more stable carbocation.
4) A water molecule abstracts a proton and the electrons collapse to quench the carbocation and
form an alkene.
what conditions are favored for alkene?
hot, concentrated acid
what conditions are favored for alcohol?
cold, dilute acid
What is a grignard synthesis (what do you produce?)
production of an alcohol with extension of the carbon chain = increase in number of carbons, by adding RMgX to carbonyl (R1-O-R2)
ex:
CH3COCH3 + CH3MgBr –> CH3COH(CH3)2
what are the steps to grignard rx?
STEPS:
1) Due to the very low electronegativity of Mg, the R group in RMgBr gains significant electron density and more or less acts as if it were a carbanion (R:-), attacking the electrophilic carbonyl carbon. This occurs in a single step, kicking the electrons in the C=O bond up onto the oxygen.
2) The negatively charged oxygen is protonated, yielding an alcohol.
can also work with electrophilic C=N, cyan groups, S=O, N=O
What is an ether?
R-O-R
what is an ester?
R-CO(OR)
what are characteristics of ether that makes it an excellent solvent?
- non reactive
-weakly polar
-short R groups so slightly soluble in water
-non polar species are soluble in ether
low boiling point because no Hydrogen bonding
when are ether most likely to react?
If the oxygen on the ether is protonated by a strong acid, it result sin an unstable intermediate that can be attacked by a nucleophile.
what are epoxides? Why would they be highly reactive?
cyclic ethers with O in triangle shape = lots of ring strain = high reactive
How would you substitute an epoxide?
Through SN1 or SN2 pathway- acid catalyzes the reaction by protonating the oxygen and making a better leaving group.
What has greater polarity: N=H or O=H ?
OH because greater electronegativity difference = stronger hydrogen bond.
What is an example of a molecule where the partial negative charge is bigger than the partial positive charge?
H2O
If an atom has a full or partial negative charge, will it donate or withdraw (take) electrons? Does Oxygen in water donate or take electrons?
donate to whatever (Atoms) they are attached to.
is Hydrogen electron donating or withdrawing?
neither
Are electrophiles electron donating or withdrawing?
withdrawing because of partial or full positive charge.
are alkenes or alkanes more electron withdrawing?
alkane.
Alkene are WEAKLY election withdrawing
Which are electron withdrawing or donating?
alkyl groups, nitro groups, cyan groups (nitriles), sulphone, amines, carboxylic acids, esters, alcohols, quaternary amines
alkyl groups --> weakly donating nitro groups --> strong withdrawing cyano groups (nitriles) ---> withdrawing sulphone -->withdrawing amines--> donating carboxylic acids--> withdrawing esters--> withdrawing alcohols--> donating quaternary amines --> strongly withdrawing
How can you predict the acidity of a molecule?
Electron withdrawing groups increases acidity –> weaker base is more stable
Do electron donating group increase or decrease basicity?
increase basicity
Why is HF a strong base?
Because F has a strong electron donating group, which make it very willing to donate to H and wants the H very much .
It’s conjugate acid would be an unstable F- atom = weak acid because unstable.
THEREFORE HF is a strong base and nucleophile (donates electron)
strong bases have elector donating or withdrawing?
donating- because they WANT the H and the conjugate acid is weaker and more unstable
stronger acids have donating or withdrawing groups?
withdrawing= good electrophile
what is mean by nucleophilicity?
refers to the “nucleus-seeking” (i.e. positive charge seeking) ability of a species, which is proportional to its electron density.
What is basicity? what increases basicity?
the number of hydrogen ions in an acid that can be replaced by a base.
electron donating group increase basicity
If a molecule has steric hindrance, will it favor basicity or nucleophilicity? why?
BASICITY because nucleophiles must have little steric hindrance.
Are electrophiles electron rich or poor?
POOR- they are electron withdrawing meaning they WANT more electrons.
If a molecule is not stable/ highly reactive, will it favor basicity or nucleophilicity?
BASICITY- full negative charge it will almost always act as a base.
4) The Grignard Synthesis is a useful step in many synthetic pathways because the attachment of the organometallic substituent to almost any carbon transforms that carbon into a good nucleophile. Given that carbons do not act as nucleophiles under standard conditions, this functionality is best explained by the:
A) high electronegativity of the metal compared to the carbon to which it is attached
B) lower electronegativity of the halogen compared to the associated metal
C) ability of metals to give up valence electrons easily
D) polarity of the halogen-carbon bond within the organometallic reagent
C
what is an hydroxyl group?
R-OH
what is the alkane functional group?
Ch3-C-C-Ch3
what is alkene functional group?
double bond C
What is the conjugated alkene?
C=C-C=C
Alkyne?
triple bond
what’s Ketone functional group?
R-C(=O)-R
what’ aldehyde’s structure?
R-C(=O)-H
carboxylic acid?
R-C(=O)-OH
ester?
R-C(=O)-OR
acid halide?
R-C(=O)-X
Amide?
R-C(=O)-NH2
anhydride?
R-C(=O)-O-C(=O)-R
Primary amine?
R-NH2
secondary amine
R-N(-H)-R
tertiary amine?
R-N(-R)-R
Primary alkyl halide?
R-C-C-X
secondary alkyl halide?
HcC-C(-X)-R
tertiary alkyl halide?
Ch3-Ch2-C(-CH3)(-X)(-R)
thiol?
R-SH
thioester?
R-S-R
ether?
R-O-R
Cis molecule has more or less net dipole? How does it increase intermolecular forces and boiling point?
more net dipole; creates greater intermolecular forces and increases boiling point.
what do grignard reaction do?
Grignard reagent reduces a carbonyl to an alcohol while adding an –R group to the carbonyl carbon
what are the reducing sugars?
A reducing sugar is any sugar that is capable of acting as a reducing agent because it has a free aldehyde group or a free ketone group.
CAN BE OXIDIZED AT HEMIACETAL GROUP by oxidizing agent such as Ag.
glucose, maltose, fructose, galactose, lactose
