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8/16/2019 Lesson 14 Acidic and Basic Character of Organic Compounds
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Lesson 14
ACIDIC AND BASIC CHARACTER
OF
ORGANIC COMPOUNDS
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Acidity Measurements
•The acidit constant! K a! "eas#$es the e%tent to &hich a B$'nst$ans(e$s a )$oton to &ate$
*A + *H,O-+
K a . ///// and )K a . 0o K a
*HA+
•Re0ati2e acidities a$e "o$e con2enient0 )$esented on a 0oa$it)3a!
2
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)3a a0#es (o$ T)ica0 OH Co")o#nds
3
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ACIDIT5 OF ALCOHOLS! PHENOL AND CARBO65LIC
Brønsted-Lowry defnition o acid
•An acid is a )$oton dono$
4
Note7 a )$oton is a hd$oen ion 8H-9
An acid in solution sets up this equilibrium:
hd$o%oni#"
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STRENGTHS OF :EA3 ACIDS
•The strengths of weak acids are measured on the )3a scale. The sm
number on this scale, the stronger the acid is.
5
Ethanoicacid
4.76
Phenol 10.00
ethanol about 16
Inc$easinAcidit
Ethano0 is so &ea; &ith a )3a o( a
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• Resonance sta
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• The dotted 0ine $e)$esents the de0oca0isation@ The neati2e cha$
cent$a00 on that end o( the "o0ec#0e to sho& that it isnt 0oca0isthe o%en ato"s@
• The "o$e o# can s)$ead cha$e a$o#nd! the "o$e sta
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• Etho%ide! the con#ate
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Ind#cti2e E((ect 7"nducti#e effect is defined as $ermanent dis$la
of shared electron $air in a carbon chain towar
electronegati#e atom or grou$.
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T)es o( Ind#cti2e e((ect 7
1@Neati2e Ind#cti2e E((ect 7
8/I e((ect! E0ect$on &ithd$a&in e((ect9when an electronegati#e atom or grou$%more electronegati#hydrogen& is attached to the terminal of the carbon chain in
com$ound, the electrons are dis$laced in the direction of the
atom or grou$.
!'(2 ) !*' ) !*((+ ) ) *l ) -r ) " ) (+ ) *+5) +
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@ Positi2e Ind#cti2e e((ect 78-I e((ect! E0ect$on $e0easin e((ect9/hen an electro$ositi#e atom or grou$ %more electro
than hydrogen& is attached to the terminal of the carin a com$ound, the electrons are dis$laced away fro
attached atom or grou$.
%*+3&3*! ) %*+3&2*+! ) !*2+5 ) ! *+3.
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Ind#cti2e e((ect is #se(#0 in e%)0ainin the st$enth o( so"e o$anic acids
a9 E((ect o( s#
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INDUCTIE EFFECTS
• E0ect$on&ithd$a&in $o#)s "a;e an a0coho0 a st$one$ acid sta
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THE INDUCTIE EFFECT IN ALIPHATIC CARBO65LIC ACIDS
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Acidit inc$eases
D#e to sta
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Basic cha$acte$ o( a0i)hatic a"ines! a"ides and a$o"ati
)3<a"ides
≈
1J
Phen0a"ine8ani0ine98an a$o"atic a"ine9
C=HJNH K@4
a""onia NH,
4@
"eth0a"ine CH,NH ,@4
eth0a"ine CH,CHNH ,@
Basicitinc$ease
A0i)hatica"ines 1b base dissociation constant
$1b !log01b
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Fo$ a0i)hatic a"ines!
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• A$o"atic a"ines8e@@ )hen0a"ine! )3
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BASICIT5 OF AMIDES
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BASICIT5 OF AMIDES
A"ides a$e e%t$e"e0 &ea; acids and a0so 2e$ &ea;
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A"ides a$e NOT
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A"ino acids contain (#nctiona0 $o#)s
The a00 ha2e a si"i0a$ st$#ct#$e the identit o( R1 and R 2a$
Q:ITTERIONS
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Q:ITTERIONS
• a witterion is a di)o0a$ ion it has a )0#s and a "in#s cha$e in its structure• a $roton from the *((+ grou$ mo#es to '+2
• amino acids eist as ?&itte$ions at a certain $+• the $+ #alue is called the isoe0ect$ic )oint• $roduces increased inter!molecular forces
• melting and boiling $oints are higher
A zwitterion is a compound with nooverall electrical charge, but whichcontains separate parts which arepositively and negatively charged.
Acid
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• amino acids $ossess acidic and basic $ro$erties due to
functional grou$s
• they will form salts when treated with acids or alkalis.
Acid
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PROTEINS
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PROTEINS
Ne#t$a0 a"ino acids
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Ne#t$a0 a"ino acids
I( the R $o#) does not contain an acidic $o#)s! the a"ino acid is ne#t$a0
Acidic a"ino acids
I( the R $o#) has "o$e acidic $o#)s then the a"ino acid is acid
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Basic a"ino acids
I( the R $o#) has "o$e