Organic Chemistry Ganley Test 2

Hydrocarbon

composed of hydrogen and carbon atoms

Saturated hydrocarbon have

no C-C pi bonds

Unsaturated hydrocarbon have

C-C pi bonds

Ethane is ___ and has a chemical formula of __

saturated, C2H6

Ethylene is __ and has a chemical formula of __

unsaturated, C2H4

Acetylene is __ and has a chemical formula of __

unsaturated, C2H2

Benzene is __ and has a chemical formula of __

unsaturated, C6H6

Formula for saturated hydrocarbons

C(n)H(2n+2)

Propane

C3H8

Butane

C4H10

Pentane

C5H12

Nomenclature

“Name Calling”

* to communicate, each unique molecule must have a unique name
* the suffix *ane* is used for saturated hydrocarbons (a.k.a. alkanes)

Why should we not use a chemicals common name?

they have little/no relation to the structure

you would need to memorize a different name for every molecule

Formic Acid

isolated from ants and named after the Latin word for ant, Formica

Urea

isolated from urine

Morphine

a painkiller names after the Greek God of dreams, Morpheus

Barbituric Acid

Adolf van Baeyer named this compound in honor of his friend Barbra

Parent chain

the longest consecutive chain of carbons

1 carbon in parent chain

meth

2 carbon in parent chain

eth

3 carbon in parent chain

prop

4 carbon in parent chain

but

5 carbon in parent chain

pent

6 carbon in parent chain

hex

7 carbon in parent chain

hept

8 carbon in parent chain

oct

9 carbon in parent chain

non

10 carbon in parent chain

dec

if there is more than 1 possible parent chain

choose the one with the most side chains attached

you want to avoid having to name complex branch

if carbons are not in a chain they are in a

cyclo ring

for cyclic acids

count the number of carbon in the ring and name it according to that number, add cyclo prefix

Cyclopropane

cyclic acid with 3 carbons

Cyclobutane

cyclic acid with 4 carons

Cyclopentane

cyclic acid with 5 carons

formula for cyclic acids

C(n)H(2n)

You cannot include carbon that are both in ___

a ring and outside a ring

use the ring to name as the parent chain

Identifying Substituents

name the same way as parent, but end in “ly”

ex: ethyl= 2 carbon chain, propyl= 3 carbon chain

cycloalkanes naming

* if ring is bigger/as big: name chain as prefix
* if chain is bigger: name the ring as prefix

common name for 1-methylethyl

Isopropyl

common name for 1-methylpropyl

sec-butyl

common name for 2-methylpropyl

isobutyl

common name for 2,2- dimethylpropyl

neopentyl

common name for 3-methylbutyl

isopentyl or isoamyl

common name for 1,1-dimethylethyl

tert-butyl

Rules for assembling the entire name

1) list substituents in alphabetical order

2) use Greek prefix for multiple identical substituents

3) prefixes are not used for alphabetical purposes, except for the prefixes “iso” and “cyclo”

use commas between ___ when naming

numbers

use hyphens between ___ when naming

letter and number

Name the molecule

Bicyclo\[2.2.1\]heptane

Name the molecule

Bicyclo\[3.1.1\]heptane

Why are there 3 numbers in the name for bicyclic compounds?

there are 3 ways to get from one bridge head caron to the other

what does it mean in you have \[3.1.1\] in a bicyclic acid name

for the first route to get from one bridge head carbon to the next, you have to pass 3 other carbons. For the second and third route, you have to pass 1 carbon.

name this compound

bicyclo\[4.3.0\]nonane

Are these molecules constitutional isomers?

yes

constitutional isomers

molecules with different structures but the same formula (differ in connectivity)

Rules for naming bicyclic compounds

1) count the total carbon in the fuse ring (parent name)

2) Number carbons (start at bridgehead carbon and number the longest carbon chain first (bridge is last)

3) use the “bicyclo” prefix

4) figure out bridgehead carbons

5) figure out bracketed numbers

2 ways to recognize constitutional isomers

1) flip one of the molecules in 3D space and rotate around its single bonds until it is superimposable on the other molecule

2) name them (same name=identical)

how to find more stable isomer

most branches= less energy= more stable

Is an isomer with more branches or less branches better for fuel

less= more energy= more reactivity

what are cracking and reforming? why do they do it with alkanes

cracking: making large molecules smaller (breaking them apart)

reforming: making small molecules bigger (adding them to each other)

they need hydrocarbons with 5-12 carbons for gas and only 19% of crude oil is suitable for gas. Using cracking and reforming methods, they can make that 19% turn into 47%.

What kind of 2D drawing is this

wedge and dash

What kind of 2D drawing is this

sawhorse (wont see often)

What kind of 2D drawing is this

newman projection (best way)

looking directly down C-C sing bong axis

keep wedges and dashes on same side

what are conformations

a different rotational state of a molecule

single bonds in molecules can rotate

Dihedral/Torsional angle

angle between atoms on adjacent C

How is VESPR useful when considering the stability of rotational conformations

* e- on the same carbon what to get as far away as possible from other e-
* similar for e- on adjacent carbons and they are still repelling each other, they will space themselves out equally
* the more spaced out the bonds are, the more stable they are

staggered conformation vs eclipsed conformation

staggered: lowest energy, more stable

eclipsed: highest energy, least stable, 0 degrees dihedral angle (maximizes repulsive interaction)

Which one is staggered? Which one is eclipsed?

Left: staggered

Right: eclipsed

In order to go from staggered to eclipsed, you have to ___ energy

absorb

torsional strain

resistance to rotation- How much energy was needed?

specifically adjacent atoms

torsional strain for ethane

12 kJ/mol; 4kJ/mol per pair of hydrogens

Will there be more eclipse conformers in room temp or high heat?

High heat because there is more energy for the molecules to absorb

does it take more energy for a pair of H to eclipse or a H and a methyl group?

takes more energy for the H and methyl group because he methyl group is bulkier

What conformation is this?

Anti

less steric hinderance

methyl groups are farthest apart

dihedral angle of 180

What conformation is this?

Gauche

methyl groups aren’t eclipsing but bump into each other a little bit

more steric hinderance

not as stable, higher energy

What conformation is this?

“totally eclipsed”

methyl groups eclipse one another

highest energy, least stable

11kJ/mol for methyl’s

What is an “eclipsed” butane conformation

when the methyl’s eclipse with hydrogens

higher energy that staggered

less energy that totally eclipsed

Cyclic alkane hybridization and bond angle?

sp3, 109.5

optimal bond angle

109\.5

2 reasons why cyclopentane in unstable

1. angle strain (60 degrees, poor sigma bond overlap; bends bonds)
2. torsional strain: all H are eclipsed

What cycloalkane is the one that has to be flat

cyclopropane

Cyclobutene properties

unstable, 88 degree bond angle, H are partially eclipsed, puckers to relieve stress

Cyclopentane properties

nonpolar “envelope”, minimal ring strain (close to 109.5 degree angle), minimal torsional strain (H slightly eclipsed)

“chair” conformation for cyclohexane properties

lowest energy, zero ring strain, no angle strain (all angles= 109.5), no torsional strain (all H= staggered)

“boat” conformation for cyclohexane properties

no angle strain, torsional strain (4 pairs of eclipsing H), steric (crowding) strain (“flagpole” interactions)

steric strain

type of torsional strain

H can be on any carbon

crowded, bump into each other

What is the highest/most unstable energy conformation of cyclohexane?

half chair

angles are being stretched= significant amount of angle strain

torsional strain- partial eclipse

\
would be planar is it existed= too high of energy for molecule to handle

“twist boat” conformation for cyclohexane properties

109\.5, relives eclipsing or some H

axial element

point straight up or down on ring

equatorial element

alternating slightly up or down around ring

if C has a H in the axial position point up, then it will also have a H in the equatorial position point down and vise versa

C will always have one of each

Monosubstuituted cyclohexane

vast majority exist in chair conformation at any given time

when energy '(45 kJ/mol) is available, it flips from one chair to another

anything that was axial is now equatorial and vise versa (direction doesn’t change; ex: axial straight up will become equatorial slightly up)

prefers methyl group in equatorial state

Chair flip

C-C single bonds rotating only

why does monosubstuituted cyclohexane prefer the methyl group in equatorial state

in axial conformation the methyl group bumps into the H in axial formation

equatorial state get the methyl group further away

1,3-dixial interactions are like gauche interactions

Equatorial interactions are like anti interactions

the larger the substituent, the __ the molecules will __ the equatorial conformation

more, favor

in disubstituted cyclohexane the dash is __ and the wedge is _

down, up

if you have 2 conformations (one with a methyl in the axial position and one in the equatorial position and vise versa) which one do you choose?

the one with the methyl in the axial position because it is smaller than the ethyl

cis:

the 2 groups are on the same side of the ring

tras

the 2 groups are on the opposite side of the ring