CH13 LEC: ALKENES, ALKYNES, AROMATICS

OSU BIOPHRM 3311

alkene definition

unsaturated hydrocarbon w/ at least 1 C=C

Alkenes are able to undergo which reaction and why?

addition rxns due to C=C presence

alkenes are ___ reactive than alkanes

more

alkenes general molecular formula

C_nH_2n

alkene suffix

-ene

what is the smallest alkene

ethene (C₂H₄)

alkyne definition

unsaturated hydrocarbon molecules with at least 1 C≡C

alkynes general molecular formula

C_nH_2n-2

alkyne suffix

-yne

smallest alkyne

ethyne (C₂H₂)

benzene is the ___ compound of the large ___ family of compounds

• parent

• aromatic

benzene compound description

contains 6-membered ring, C or other atoms, w/ alternating single and double bonds

heterocyclic aromatic compounds definition

• when elements, other than C, are also members of a ring structure

  • also called heterocycle rings or heterocyclic compounds

5 nucleotide bases

• adenine, guanine, cytosine, thymine, uracil

nucleotide bases purpose

form components of DNA & RNA

2 categories of nucleotide bases

• pyrimidines

• purines

pyrimidines definition

a single 6-membered ring (2 Cs replaced by 2 Ns)

purines definition

pyrimidine ring fused to a 5-membered ring

recognize this structure

purine (parent)

recognize this structure

adenine (A) (DNA, RNA)

recognize this structure

guanine (G) (DNA, RNA)

recognize this structure

pyrimidine (parent)

recognize this structure

cytosine (C) (DNA, RNA)

recognize this structure

thymine (T) (DNA, some RNA)

recognize this structure

uracil (U) (RNA)

3 amino acid sidechains

• phenylalanine, tryptophan, tyrosine

  • also called: aromatic amino acids

recognize this structure

general amino acid structure

amino acid links to ___ from a central C

4 groups

what determines the key characteristics of an amino acid?

the sidechain

recognize this structure

phenylalanine

recognize this structure

tyrosine

recognize this structure

tryptophan

what is the relationship b/t tyrosine and phenylalanine?

tyrosine is derived from phenylalanine — making these two interchangeable to some degree in proteins and metabolism

why can you not add more Hs to a benzene ring?

b/c there is only 1.5 e- in the double bond

resonance structures of benzene

• the e- are delocalized or shared throughout the ring structure — across the single & double bonds

• contributes to increased stability, resulting in lower reactivity

• can exist as 2 structures, A. and B., and written as C.

saturated molecule definition

• all Cs are linked together by only single bonds

• each C bonds to 4 groups

• no more Hs can be added

unsaturated molecule definition

• contains one or more double or triple bonds

• addition Hs can be incorporated, leading to conversion of a multiple bond to a single bond

  • every time you make a C=C, 2 Hs are removed

Addition rxn definition

for unsaturated hydrocarbons, more Hs can be added to multiple bonds to form single bonds and saturated hydrocarbons

in naming alkenes and alkynes, number the chain starting from ___.

the end closer to the multiple bond

in naming alkenes and alkynes, use the ___ to indicate the location of the functional groups

smaller number

in naming alkenes and alkynes, the longest chain chosen for the root name must include ___.

both C atoms of the double/triple bond, even if the chain is longer w/out — you choose the shorter chain that includes these bonds

in naming alkenes and alkynes, if a double/triple bond and an alkyl substituent are both present, the ____ has the lowest number.

alkene/alkyne group

• priority to family name first, then to the substituent

in naming alkenes and alkynes, if the double/triple bond is equal distance from each end, number so the ___ has the lowest number.

1st substituent

in naming alkenes and alkynes, if more than one double/triple bond is present, indicate their position by using the ___.

number of the 1st C of each bond, and use the suffix — -diene, triene, tetraene, diyne, triyne, tetrayne, etc.

trivial or common names definition

informal names given to compounds that are often simpler and more user friendly than their IUPAC names

Common name of ethene (H₂C=CH₂)

Ethylene

common name of propene (CH₃CH=CH₂)

propylene

common name of ethyne (HC≡CH)

acetylene

cycloalkenes definition

hydrocarbons that contain 1 or more C=C in a ring

in naming cycloalkenes, number the double bond Cs ___, and the 1st substituent has ___.

• 1 & 2

• the lowest possible number

in naming cycloalkenes, if there is an alkyl substituent on one of the C=C, that C is ___.

• #1

• NOTE: sometimes this can lead to a deviation from the Lowest Sum Rule, and you end up choosing the larger sum b/c the positioning is prioritized. (see pic for example)

in naming aromatic compounds w/ 1 substituent, substituted benzenes are named using the substituent as ___.

the prefix followed by -benzene as the parent. no number is needed for mono-substituted benzenes b/c it is always 1.

recognize this structure by its common & IUPAC name

• common name: toluene

• IUPAC: methylbenzene

recognize this structure by its common & IUPAC name

• common name: phenol

• IUPAC: hydroxybenzene

recognize this structure by its common & IUPAC name

• common name: aniline

• IUPAC: aminobenzene

ortho (o) definition

indicates position of 2 substituents on benzene ring: 1,2— (2 substituents next to each other)

meta (m) definition

indicates position of 2 substituents on benzene ring: 1,3— (separated by one carbon)

para (p) definition

indicates position of 2 substituents on benzene ring: 1,4— (across from each other on the ring)

phenyl group definition

what benzene rings are called when they act as a substituent group attached to another parent compound

conformers arise from what?

unrestricted rotation around a C—C single bond

T/F: 2 molecules having the same structure do not always have the same IUPAC name.

False; they always do

in cis— or trans— structures, the C=C is ___ and cannot be ___.

• rigid

• rotated unless by breaking the double bond

know this is cis and which is a trans structure

another name for cis-trans isomer

geometric isomer

cis means ___ side.

same

trans means ___ side.

opposite

cis shape

bent

trans shape

more linear

When one of the C=C is bound to the ___, cis-trans isomerism is impossible.

same group

cis-isomer definition

when identical or larger groups are on the same side of the C=C

trans-isomer definition

when identical or larger groups are on the opposite sides of C=C

the formation of cis-trans isomers in alkenes depends upon the___.

groups bound to C=C

alkenes w/ —C=CH2 ___ as cis-trans isomers

do not exist

alkenes w/ —C=CR2, where the R-groups are identical, ____ as cis-trans isomers

do not exist

what are the five major reactions

addition, elimination, substitution, rearrangement, oxidation & reduction

addition reaction definition

a reaction X—Y is added to the multiple bond of an unsaturated reactant to yield a saturated product

name this reaction: 2 reactants form 1 product

addition rxn

elimination reaction definition

saturated reactant yields an unsaturated product by losing a group from each of the 2 adjacent Cs; forming a double bond in place of a single bond

name this reaction: 1 reactant forms 2 products

elimination reaction

why type of reaction is a dehydration reaction?

elimination reaction

dehydration reaction definition

removal of H2O

what is this reaction: alcohol → alkene + water

elimination reaction: dehydration of alcohols

substitution reaction definition

an atom or group of atoms in a molecule is replaced by another atom or group of atoms in a molecule

name this reaction: 2 reactants form 2 products

substitution reaction

a common substitution rxn of alkanes is ___.

halogenation

rearrangement reaction definition

type of o-chem rxn in which the structure of a molecule is reorganized to form a new isomer. the atoms/groups shift to different connectivity / positions w/out adding or removing any atoms. 

name this reaction: 1 reactant forms 1 product

rearrangement reaction

the reactants and products of a rearrangement reaction are ___.

constitutional isomers

oxidation reaction definition

addition of O atom(s) OR removal of H atom(s)

reduction reaction definition

removal of O atom(s) OR addition of H atom(s)

due to the presence of multiple bonds, alkenes and alkynes are ___ than related alkanes

more reactive

the most common rxns involving C-C multiple bonds are ___.

addition reactions

common addition rxns involving C—C multiple bonds

• hydrogenation

• halogenation

• hydrohalogenation

• hydration

benzene doesn’t undergo ___ b/c that would necessitate disrupting its delocalized e- system, resulting in a loss of its inherent stability

addition reactions

hydrogenation reaction definition

H is added to a multiple bond yielding a saturated product

• alkenes and alkynes react w/ H to yield alkanes

halogenation reaction definition

the addition of a halogen (Cl2, Br2, etc.) to an alkene yields a dihaloalkane

hydrohalogenation reaction definition

alkenes react w/ hydrogen halides (HBr, HCl, etc.) to yield alkyl halides (IUPAC haloalkanes)

hydration reaction definition

alkenes react w/ H2O to yield alcohols

Markovniko’s Rule

in the addition of H—X (such as HBr, HCl, or H2O) to an asymmetrical alkene, the H will add to the C of the double bond that already has the greater number of Hs, while the X will add to the C w/ fewer Hs.