chapter 4: nomenclature and conformations of alkanes and cycloalkanes

alkanes

C(n)H(2n+2)

sp3 / tetrahedral

cycloalkane

C(n)H(2n)

sp3/tetrahedral

simple ring, no extra bonds

substituents

extensions of the main chain

- end in -yl

types of substituents: 3 carbons

- propYL (carbons in a chain)
- ISOpropYL (isomer/bunny ears)

types of substituents: 4 carbons

butyl: straight
isobutyl: bunny ears at the end
sec-butyl: secondary carbon
tert-butyl: tertiary carbon

types of substituents: 5 carbons

neopentyl: butyl plus an extra carbon

parts of a systematic name

parent name: longest carbon chain
suffix: indicates which functional group is present
prefix: identity, location, and number of substituents

name branched chain alkanes

- find the longest chain

- give each substituent a name and number

- if one substituent, give it the lowest number on the chain. for 2 or more do the same and put alphabetically.

- when substituents are on the same chain use than number twice

- for identical substituents (ex 2 methyls) use prefixes like di, tri, tetra

when there are parent chains of equal length, choose the one with the greater number of substituents

list substituents in alpha order (not including prefixes or when when hyphenated)

when branches occur at an equal distance from either end of the chain, choose the lower set (ex: pick 2,3,5 over 2,4,5)

how to name branched alkyl groups

- find the longest chain

- give each substituent a name and number

- if one substituent, give it the lowest number on the chain. for 2 or more do the same and put alphabetically.

- when substituents are on the same chain use than number twice

- for identical substituents (ex 2 methyls) use prefixes like di, tri, tetra

when there are parent chains of equal length, choose the one with the greater number of substituents

list substituents in alpha order (not including prefixes or when when hyphenated)

when branches occur at an equal distance from either end of the chain, choose the lower set (ex: pick 2,3,5 over 2,4,5)
branched substituents are also named as their alkyl group names (ex iso, sec, tert)

how to name cycloalkanes

cyclo- (number of carbons)-ane
ex: 5 = cyclopentane

- ring is the paren t hydrocarbon unless the substituent has more carbons than the ring [( when sub is larger: 1- cyclobutYLpentANE) (when parent is smaller: 1-methylcyclohexane)]

- when more than one substituent cite in alpha order, the first one will be numbered as 1
the exception to this is if you number them the other way around and produce lower set of numbers (ex: 2m, 4e, 1p >>> 1p, 3m, 4e7

cis-isomer

functional groups on same side

transisomer

functional groups on different sides

bicycloalkane

compound containing 2 fused or bridged rings

parts:
- bridgehead: common carbons to both rings
- bridge: each bond or chain of atoms connecting bridgehead
- bridged vs. fused: bridged rings have one or more carbons in the bridge (below); fused rings have zero carbons in the bridge

bridges are signified with numbers (descending)
- ex you can have a one carbon bridge, 2 carbon bridge etc

named "bicyclo[#.#.#]...ane"

bicycloalkane nomenclature

- identify the parent name

- number the carbons (around the largest bridgehead, 2nd largest and smallest, give substituent the lowest number)

- identify the bridges, bracket them

- add substituents

alcohol nomenclature

end in -ol

- find largest carbon chain containing C bonded to OH group

- number carbon chain giving OH the lower number

- name other substituents

- add diol/triol when more than one hydroxy group

5-methyl-3-hexanol/5-methylhexa-3-ol

cyclic alcohol nomenclature

cyclo- / -ol

- OH gets the number 1 position; it isn't required to number the 1 either

- can put number before -OH or in front

alkenes nomenclature

- find largest carbon chain containing both the carbons on the double bond

- number carbon chain, give the double bond the lowest number

- add substituents, alphabetize

- when more than 1 double bond, change the "-ene" to "-adiene" or "atriene"

- double bonds are usually located between C1 and C2. the 1 is usually omitted. the ring is numbered to give the first sub the lowest number (if sub and DB are on same carbon , it is 1)

alkenols

compounds containing double bonds and hydroxys

cycloalkenes

allyl group

C=C-C-C

vinyl group

C=C-C

naming alkynes

-yne ending

-choose the longest parent chain containing both atoms in the triple bond, giving the triple bond the lowest number

- zdd substituents, alphabetize

- 2 triple bonds: diyene

- 3 triple bonds triyene

- "enyne": double bond and triple bond

alkyl halide nomenclature

always named as a substituent

Cl - chloro, F,-fluoro Br-bromo, I-iodo

- find the longest parent chain

- give the lowest number

alphabetize

conformations

different arrangements of atoms that are interconverted by rotation about single bonds

dihedral angle

angle separating a bond on one atom from a bond on an adjacent atom

- 0 dihedral angle- "eclipsed conformation" when the hydrogen groups on adjacent atoms are lined up on each other

- 60 dihedral angle- "staggered conformation" the furthest that the hydrogens on adjacent atoms can be spread apart. these have the lowest energy conformation

sigma bonds ------ rotate, pi bonds ------ rotate

can; cant

newman projections

convention for drawing end-on representation of conformations

how to draw newman projections

- look directly down at the C-C bing (end on) and draw a circle with a dot in the center to represent the carbons of the bond

- draw the bonds on the front C as 3 lines meeting the center. next draw the bonds on the back c as 3 lines coning out of the edge of the circle (staggered first)

- add the atoms on each bond

- bods can be anything ex: hydrogens, methyl groups

anti conformation

(newman conformation) a staggered conformation with 2 larger groups 180 degrees from each other

lowest energy

gauche conformation

(newman conformation) a staggered conformation with 2 larger groups 60 degrees from each other

eclipsed conformation

(newman conformation) - 0 dihedral angle; when the hydrogen groups on adjacent atoms are lined up on each other

highest energy when large groups right next to each other

staggered conformation

- 60 dihedral angle; the furthest that the hydrogens on adjacent atoms can be spread apart. these have the lowest energy conformation

lowest energy when large groups 180 degrees away from each other (anti)

steric strain

an increase in energy resulting when non bonded atoms are forced too close to one another (basically- when they pass each other as they rotate, the energy increases)

the relative energies of the individual staggered conformations depends on the amount of steric strain (ex more steric strain when 2 methyl groups come in contact rather than when 2 hydrogens come in contact)

gauche conformations are higher energy than anti conformations because of steric strain

barrier to rotation

the energy difference between the lowest and highest energy conformations due to steric strain

what happens when you add more substituents to your newman conformations?

the energy will be greater

zigzag skeletal structures

the lowest energy conformations in alkenes are found in these structures because all groups are staggered and the large groups are anti

ring strain in cycloalkanes

is a combination of the following

- torsional strain: forced eclipsed conformation

- angle strain: an increase in energy when bond angles deviate from 109.5 where it is ideal for sp3 hybridized carbons

what is they reality of the structure of cycloalkanes?

they pucker/distort their shapes in order to alleviate ring strain

ex- cyclohexanes will pucker to go from 120 degrees apart to 109.5 degrees

chair conformation

most stable conformation of cyclohexene- eliminated angle strain (all C-C bonds 109.5 degrees) and torsional strain

each C in cyclohexenes have 2 different kinds of bonds to substituents (h or other groups)
- axial bonds: point up and down
- equatorial: point out

cyclohexene boat confromation

one side of the chair conformation will flip upwards

- flagpole positions: at the tips of the boat pointing inward, too much overlap causing steric strain

- not as stable because eclipsing

homologous series

when looking ar physical properties, a series of compounds in which each member differs from the next by a constant unit is called this

members of these series are called homologues

boiling points of alkanes and cycloalkanes

branching an alkane lowers the boiling point while in unbranched alkanes, when the molecular weight increases the size and molecular surface area increase thus dispersion forces increase and more energy is required to separate molecules (higher bp)

in addition to this, cycloalkanes will have higher boiling points than alkanes

melting points of alkanes and cycloalkanes

in unbranched alkanes, you cannot see the melting point as smoothly as you would on the plot for boiling point. however, is you separate the curve with even and odd amounts of carbons, there is a smooth increase in the melting point. this is because when there are even amounts of carbons, the atoms pack more evenly in a crystalline state. thus attractive forces are greater and melting points are higher

in addition to this, cycloalkanes will have higher melting points than the open chains

mono-substituted cyclohexanes

to minimize the energy caused by steric strain, the ring can flip to put bulkier substituents in equatorial positions

molecules are changing conformations to minimize 1,3,-diaxial interactions of bulky substituents

- big substituents will try to be in equatorial position**

degree of unsaturation / index of hydrogen deficiency

is the number of pi bonds and cyclic structures in a molecule

- note that a double bond has 1 pi bond while triple bonds have 2

- unsaturated hydrocarbons have less than the maximum number of hydrogen atoms per carbon (2n+2) [ alkenes/alkynes]

calculating degree of unsaturation

follow the general formula of a hydrocarbon (C[n]H[2n+2-2x])

2n+2 -2x; x = degree of saturation

- n = number of carbons
- when heteroatoms are present: ignore oxygen, add 1 for each halogen (F, Cl, Br, I) to the number of H's; subtract 1 from H for each N present

hydrogenation

a reaction in which a hydrogen adds to a double or triple bond. often completed trhough the use of a metal catalyst like Platinum Pt, palladium Pl, or nickel Ni.

the alkene and alkynes will react with hydrogen in order to produce alkanes