Intro to Organic Chem Flashcards by Kelsey Con

describe characteristics of a sigma bond

direct overlap of hybridized orbitals along the axis between 2 atoms
very strong and stabilizing
1 sigma bond in every bond

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describe characteristics of a pi bond

overlap of parallel p orbitals
weaker than a sigma bond
one in a double bond and 2 in a triple bond

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describe the relationship of potential energy with the type of bond

as bond strength increases more energy is required to break the bond therefore the potential energy LOWERS
ex sigma bond has a lower potential energy than a pi bond

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describe the relationship of bond length and bond strength

inversely proportional

longer the bond the weaker it is

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describe the relationship between bond dissociation energy and number of bonds

bond dissociation energy increases as the number of bonds between atoms increases ***not double the amount of energy tho because a pi bond isn’t as strong as a sigma bond
double and triple bonds prevent free rotation around the axis

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how do you draw a lewis dot structure

count valence electrons based on group # and the charge of the ion
identify central atom, usually least electronegative
add other atoms around central atom
complete the octet for central atom then atoms surrounding

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what are some exceptions to the octet rule

boron and aluminum ok with incomplete octet

phosphorus and sulfur can accommodate more than a full octet

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how do you calculate formal charge

# of valance electrons in free atom (group #) - # of lone pair electrons - # of bonds
one lone pair = 2
a double bond =2

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how are resonance structures formed

movement of lone pairs and pi bonds

can’t move sigma bonds

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how to determine major minor and intermediate resonance structures

1) full octet
2) minimum number of formal charges
3) negative formal charge on the most electronegative atom
4) minimum separation between opposite formal charges

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what do a vertical and horizontal line indicate in a fisher projection

horizontal = out of the page
vertical = into page

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how do you use VSEPR to predict basic geometry

draw the lewis structure and determine the number of groups which is the # of atoms connected to the central atom (double bond and triple bond still =1) + lone PAIRS on the central atom

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geometry, angle, and hybridization of 2 groups

linear
180
sp

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geometry of 3 groups

trigonal planar
120
sp2

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geometry of 4 groups

tetrahedral
109.5
sp3

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geometry of 5 groups

trigonal bipyramidal
90 + 120
sp3d

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geometry of 6 groups

octahedral
90
sp3d2

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how do molecular geometries differ from basic

if there are no lone pairs on the atom the basic will be the same as the molecular
lone pairs have stronger repulsion so it will decrease the bond angle bonding electrons and have more of an angle from the non bonding lone pair
ex. trigonal planar with one lone pair will have a bond angle <120 between the bonding electron pairs

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how does delocalization affect stability

delocalized electrons extend over multiple bonds and atoms which is shown in resonance structures
increases stability

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what are huckels rules to determine if a species is aromatic

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contains a total of 4n + 2 PI electrons
sp2 hybridized carbons
planar monocyclic

how does nitrogen contribute to aromaticity

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if N has 3 sigma bonds the lone pair will contribute to the pi system
if N has 2 sigma bonds and a pi bond the lone pair will not contribute to the pi system

how do oxygen and sulfur contribute to aromaticity

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one lone pair will contribute to the system and one will not

alkane conformational isomers different structures are represented by Newman projections as they rotate about their carbon carbon single bonds explain the different levels of energy

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anti staggered is the most stable and has the lowest energy

eclipsed is the least stable and has the highest energy

define chiral

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any object that can’t be superimposed on its mirror image

what are the 2 features of a chiral carbon

sp3 hybridized | bonded to 4 different atoms or groups

how do you rank substituents attached to a chiral centre according to can infold prolog rules (ie when determining absolute configuration)

highest atomic # takes highest priority if two atoms are the same look to the next atom until a difference is found double bonds take high priority because they are bonded twice to that atom**doesnt apply to organic reactions

how do you determine absolute configuration

rank substituents ignore the lowest if faced away from the viewer clockwise = R counterclockwise = S if the lowest is faced toward the view the answer is the opposite

what is the difference between constitutional isomer and stereoisomer

constitutional - structural, different connectivity | stereoisomer - different arrangement in space such as enantiomer and diastereomer

difference between enantiomer and diastereomer

enan - non superimposable mirror image, opposite configuration at every chiral centre diaster - not mirror image, have 2 stereocenters and differ at at least one of them

cis vs trans isomer (di substituted alkenes only)

cis (Z) - two substituents on the zame zide of the double bond trans (E) - two substituents are on the opposite side of the double bond

tri and tetr substituted alkene naming system

1 rank the 2 substituents priority z isomer if two high priority on the same side e isomer if opposite side

what are enantiomers

non super imposable mirror images

3 important features of enantiomers

opposite stereochemistry at all stereocentres identical chemical and physical properties except rotated plane polarized light with equal and opposite rotations*** react differently in a biological chiral environment

what is a racemic mixture

50:50 of 2 enantiomers | result in no net rotation of plane polarized light

how can enantiomers be separated

resolution: add enantiomerically pure reagent to produce a diastereomeric salt. since they are diastereomeric salts they have different physical properties and can be separated by physical separation chiral chromatography: stationary phase that is chiral and will only bond to R or S then perform chromatography

what is a diastereomer

stereoisomer that isn't a mirror image | have 2 stereocenters and differ at a min of one stereomer

how can you determine the max number of stereoisomer of a molecule

2 ^n | where n = number of chiral centers

which way does dextrorotatory rotate light

right (clockwise) | +

which way does levorotatory rotate plane polarized light

left (counterclockwise) | -

how is the direction in which an enantiomer rotates plane polarized light determined

by experiment only | it is not related to the absolute configuration of R or S

what characteristics are required to determine if a compound is meso

min of 2 stereo centres plane of symmetry in the molecule both halves are mirror images of each other

how do mess compounds rotate plane polarized light

they don't

how can diasteromers be separated

they have different chemical and physical properties so can use recrystallization, boiling, column chromatography

in a liquid liquid extraction a separatory funnel is filled with organic and aqueous solvent where are each layers found and what molecules will be found within the layers

aqueous on the bottom containing small polar molecules, strong acids and bases, salts **charged molecules organic rises to the top containing large or less polar molecules

describe the stationary and mobile phase in TLC

stationary phase = silica gel or aluminaVERY POLAR mobile phase = solvent, always less polar than the stationary phase. changing the solvent can change how far the components travel but the less polar one will always travel farther

how can you tell polarity in TLC

move further up the plate = more non polar | stay closer to the bottom stationary phase = more polar

give a brief description of how to preform TLC

get a silica coated plate and dab a small amount of solvent at the origin put in COVERED vessel to prevent evaporation with some solvent at the bottom when solvent front reaches the top mark a line and leave dry put under UV light

Rf formula in TLC *** what do the values mean

distance compound travelled / distance to solvent front | smaller = more polar , travels slower

Intro to Organic Chem Flashcards

(48 cards)