135A organic - introduction Flashcards by charlotte Burkert

what is the structure of a carbocation

planar 120°, sp2 hybridised, empty p orbital

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incomplete octets are allowed in lewis structures e.g. BH3 but what does this mean about the molecule?

highly reactive (BH3 will form B2H6)

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what elements can sometimes hold 10-12 electrons even though lewis formula only allows for 8

second row Na—> Ar

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What will the charge be on N (P5)

In this diagram N has 4 electrons belonging to it, but it should have 5 in its natural state; has a charge of +1

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What will the charge be on C (P4)

In diagram has 4 belonging to it and has 4 in its natural state; will be neutral

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Why is a tertiary carbocation stable

hyperconjugation the bonding pair of σ electrons in adjacent C-H bonds can align with the empty p orbital of the carbocation. Carbon adjacent to c+ develops partial positive charge; + charge no longer localised on carbocation

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Lewis structure of the methoxide anion

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define electronegativity

ability of atoms to attract electrons in a covalent bond towards themselves

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how to represent the polar bond of C-F

arrow goes towards most electronegative

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how to represent the polar bond of C-Li

arrow goes towards most electronegative

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what is the inductive effect

shifting of electrons in bonds in response to electronegativity of nearby atoms

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trend in atom size across a period

decreases

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if this molecule is drawn with balls and sticks, nitrogen is drawn smaller than boron.

atomic radius decreases across period/ has higher Z effective because more protons but same electron shells/ its electron cloud is smaller

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draw molecule polarity diagram for water

lone pairs have the highest electron density, arrows go from high ED to low ED

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draw molecule polarity diagram for CO2

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define the terms to work out the dipole moment

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Why does CF4 have no dipole moment

polar bonds but due to geometry has no positive or negative end

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Why does a polar substance not dissolve in a non-polar solvent?

only substances with similar dipole moments will dissolve in each other

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If there is a high difference in electronegativity between two atoms is there a large or small degree of covalent character

lower % (more ionic)

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equation for pKa

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equation for pH

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equation for pOH (OH- concentration)

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higher pKa = lower/higher Ka = weaker/stronger acid

higher pKa = lower Ka = weaker acid

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why is do we usually write H3O+ in equations for dissociation not H+

H+ is very reactive and almost always reacts further with more H2O to make H3O+

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why for the Ka of this reaction would you leave H2O out

so little is used up that its concentration is basically constant

what does Ka describe

acidity constant in water at 25°

what does the sum of pH and pOH equal

Kw equation

Kw = [H3O+][OH] = 10-14

what is Kb

basicity constant (strength of base) at 25°

what does a pKa below 1 mean

acid is fully dissociated

what does a pKa above 1 mean

acid partially dissociated

the equilibrium constant always favours the side with the stronger/weaker aid (in an acid base reaction)

weaker acid (equilibrium will lie to right by factor of 10^11 (15-4))

Inverse strength rule- the stronger acid will have a stronger/weaker congruent base

stronger acid = weaker con base

will this be a strong or weak acid

strong acid/ less e- density around the COOH group as **electron withdrawing** groups (want less e- density because the molecule has to attract a negative species to take H+ close to it)/ more stable anion **favours dissociation**

will this be a strong or weak acid

weak acid/ more e- density around COOH/ CH3 are **electron donating**/ **disfavours dissociation**

Lewis definition of a nucleophile and electrophile ( in terms of electrons)

nucleophile- electron pair donor electrophile- electron pair acceptor

Bronsted-Lowery definition of a nucleophile and electrophile (in terms of protons)

nucleophile- proton acceptor electrophile- proton donar

what is the difference between a Bronsted-Lowery proton and a Lewis acid

All Bronsted-Lowery acids **must contain a proton**

single/double bonds are shorter

double bonds are shorter

two resonance structures for a methanoate ion

what average charge does each oxygen atom have in these resonance structures

-2/3 (-1)+(-1) / 3 atoms = -2/3

are resonane structures real

no- the real molecule is an average of all resonance structures (this hybrid will be **lower in energy** than either individual resonance form

Why does more resonance structures= more stable

more ways for e- to be distributed/ charge is less localised to one area of the molecule/ more partial charges across more atoms

why are these two not resonance structures

If we move two electrons over, N would have 12 electrons around it (N has a lone pair on it too)

resonance structure of this benzene ring

the actual structure of benzene in a hybrid between the two and just form a delocalised ring due to stability

what charge would each oxygen atom have

(-1)+(-1) / 4 atoms = -0.5

Rules of drawing resonance structures

1. atoms must be in the same place 2. cannot break octet rule 3. have to have the same charge

Are these resonance structures

no- chlorine has moved place

Are these resonance structures

no- the H has moved places

What does the nitrogroup look like

which structure will contribute more to the resonance hybrid

It is the most stable structure/ more stable to have the - on the oxygen atom rather than the carbon because oxygen has higher electronegativity

Why are carboxylic acids stronger acids than alcohols

When the H is removed the COO- anion is much more stable (**shared negative charge**) than the O- (must take all the negative charge)

what are tautomers

structures in equilibrium with different geometrics and different arrangements of nuclei and electrons

What generally moves in a tautomer

(the lightest atom) Hydrogen

What is the tautomer of this molecule

(ignore arrows)

Where does the curly arrow have to come from in a double bond

the π area as this is the area that donates the electrons

reaction of cyclohexane with ammonia

positive charge on N=nitrogen has 4 electrons belonging to it but 5 in its natural state

is a Lewis acid/base an electron pair donor/acceptor

acid- electron acceptor (donates proton)- electrophile base- electron donor (accepts proton)- nucleophile

Some things can react as a base or a nucleophile. How is OH- reacting as a base

Lewis base- electron donor/ proton acceptor. This OH- is **accepting a proton**

Some things can react as a base or a nucleophile. How is OH- reacting as a nucleophile

nucleophile- electron donor. In this case the OH- is donating itself (electrons)

what does basicity and nucleophilicity mean

basicity- affinity towards a proton nucleophilicity- affinity towards carbon (ones that have a partial or full positive charge)

Here is the OH- acting as a base or nucleophile

nucleophile- it donates electrons (itself)

When drawing mechanism reactions between H+ in solution we do not use H+ as this is very reactive and doesn't exist for long in a solution; what do we write instead

as H3O+

How would these two molecules react

How would these two molecules react now that there are CH3 groups attached instead of R groups

If there are hydrogens around a strong base (alkyl lithiums), **Carbon can act as a base**(accepts a proton). Electrons move from the C to form a C=C and this forces the electrons onto O

MO of a C=C bond

show how sp3 hybridisation forms in a CH3 molecule

is OMe electron withdrawing or donating

donating