aliphatic amines in physics

7/28/2019 Aliphatic Amines in physics

1/6

C H A P T E R 8A l i p h a t i c A m i n e sNH 2 Stretching Frequen cies for Aliphatic Am inesNH 2 Wag Freq uencies for Aliphatic Am inesNH 2 Bending for A lkylaminesRaman Da ta for Pr imary Am inesChemica l Reac tions of Alkylamines Conta in ing NH 2 or NH GroupsSecondary Aliphatic AminesReferencesTablesTable 8-1Table 8-2 147 (144)148 (145)

14314414 514 514 5146146

*Numbers in parentheses indicate in-text page reference.

In t he d i s c us s i on o f a l i pha t ic a m i ne s i t is ne c e s sa ry t o c o i n sym bo l s fo r e a c h t ype o f a mi ne , a ndt h i s wa s e s t a b l i she d i n R e fe re nc e (1 ) .The s ym bo l s P , S , a nd T are u se d f i rs t t o de no t e p r i ma ry , s e c onda ry , a nd t e r t i a ry a mi ne s (NH 2 ,NH, a nd N ) , r e spe ct i ve l y . The sym bo l s P ', S ', a nd T ' are u se d s e c o nd t o de no t e t he s t ruc t u re o f thea l ky l po r t i on o f t he a mi ne [R C H2- , (R )2C H , a nd (R )3C ] fo r the p r i ma ry , s e c onda ry , a nd t e r ti a ry ,r e spec t ive l y . F o r e xa mp l e , d i m e t hy l a m i ne w ou l d be de n o t e d a s S P~ P , d i so p ro py l a mi n e a s SS~S ,me t hy l a m i ne a s P P ', a nd t e r t -bu t y l a mi n e a s P T t.

N H 2 S T R E T C H I N G F R E Q U E N C I E S F O R A L I P H A T I C A M I N E SI n t h e v a p o r p h a s e , v a s y m . N H 2 a n d v s y m . N H 2 h a v e w e a k I R b a n d i n te n s it y , a n d o f t e n t h ev a sy m . N H 2 m o d e i s n o t o b s e r v e d . T h e v a s y m . N H 2 m o d e is a s s i g n e d i n t h e r e g i o n 3 4 0 4 -3 4 2 2 c m - 1 a n d v s y m . N H 2 i n t h e r e g i o n 3 3 4 0 - 3 3 6 1 c m - 1 . I n m o s t c a se s, v s y m . N H 2 h a s m o r ei n t e ns i t y t ha n va sym. N H 2 (1 ) .

Howe ve r , t he s i t ua t i on i s r e ve r se d i n t he 2 -a l koxye t hy l a mi ne s e r i e s , bu t i s no rma l i n t he 3 -a l k o x y p r o p y l a m i n e s e r i e s . T h u s , t h i s i n t e n s i t y r e v e r s a l r e s u l t s f r o m w e a k i n t r a m o l e c u l a rh y d r o g e n b o n d i n g b e t w e e n a n N - H p r o t o n a n d t h e f re e p a i r o f e l e c tr o n s o n t h e 2 - a l k o x yo x y g e n a t o m .

143


2/6

1 4 4 Aliphatic AminesP r i m a r y a l ip h a t ic a m i n e s w i t h P S ' s tr u c t u r e e x h i b i t v s ym . N H 2 i n t h e r e g io n ~ 3 3 3 0 -

3 3 4 0 cm - 1 , an d th i s I R b an d i s weak . W h e n o b se r v ed , v a sy m . N H 2 i s a s s ig n ed in t h e r eg io n~ 3 4 0 0 - 3 4 2 2 c m - 1 .

Pr im ar y a l ip h a t i c am in e s w i th PT ' s t r u c tu r e ex h ib i t v sy m . NH 2 in t h e r eg io n 3 3 2 2 - 3 3 3 5cm - 1 , an d v a sy m . NH 2 wh en o b se r v ed in t h e r eg io n 3 3 9 5 - 3 4 0 0 cm - 1 . Bo th I R b an d s a r e weak .I n su m m ar y , t h e v N H 2 f r eq u en cy p r o g r e ss in g in t h e o r d e r PP ' , PS ', an d P T ' i s sh o w n h e r e ( 1) "

S t r u c t u r e v a s y m . N H 2 c m - 1 v s y m . N H 2 c m - 1 T y p eR - C H 2 - N H 2 3 4 0 4 - 3 4 2 2 3 3 4 0 - 3 3 6 1 P P '( R - ) C H - N H 2 ~ 3 4 0 0 - 3 4 2 2 3 3 3 0 - 33 4 0 P S'( R - ) C ( - N H 2) 3 3 9 5 - 3 4 0 0 3 3 2 2 - 3 3 3 5 P T 'H O - C H 2 - C H 2 - N H 2 3 46 5 3 3 42 P P 'H O - C H 2 - C H C H 3 - N H 2 3 4 14 3 3 48 P S'HO-CH2-C(CH ) 2 - N H 2 3 4 0 0 3 3 3 5 P T '

N H 2 W A G F R E Q U E N C I E S F O R A L I P H A T I C A M I N E ST ab le 8 .1 l i s ts IR v ap o r - p h ase d a t a an d a ss ig n m en t s f o r p r im ar y a lk y lam in es . T h e c o m p o u n d swi th P P ' s t r u c tu r e ex h ib i t a s t r o n g r e l a t i v e ly b r o ad b a n d in t h e r eg io n 7 6 4 - 7 8 0 c m - 1 . T h eab so r b an ce ( A) r a t io s : ( A) [ NH 2 wa g ] / ( A ) [ v sym . C H 2] an d ( A) [ NH 2 wa g ] / ( A ) [ C H 2 b en d ]sh o w th a t t h e v a lu e s d ec r ea se p r o g r e ss in g in t h e o r d e r C 2 to C1 9 . T h i s p r e su m a b ly in d ica t e s t h a t(A) fo r N H 2 wag is re la t ive ly const an t , and tha t (A) fo r vsym . C H 2 and (A) fo r C H 2 ben din c r ea se a s t h e n u m b er o f (CH2 ) n in c r ea se s . Co r r e l a t io n s su ch a s t h e se a r e v a lu ab le i n sp ec t r a -s t r u c tu r e i d en t i f i c a t io n o f u n k n o w n a l ip h a t i c am in es .

T h e c y c lo a lk y am in es w i th th e s t r u c tu r e PS ' ex h ib i t NH 2 wag in t h e r eg io n 7 5 5 - 7 8 5 c m - 1 , a n dwi th th e ex cep t io n o f cy c lo h ex y lam in e in c r ea se in f r eq u en cy a s t h e cy c lo a lk y l r i n g in c r ea se s i ns i ze f r o m C 3 to C 8 . T h e ab so r b an ce ( A) r a t i o s f o r N H 2 wa g /v sy m . CH 2 an d NH 2 w ag /C H 2 b en da l so d ec r ea se in v a lu e a s t h e n u m b er o f CH 2 g r o u p s in c r ea se f r o m 3 to 8 .

T h e NH 2 wag f o r a lk y lam in es i s al so a f fec t ed b y th e s t r u c tu r e o f th e a lk y l g r o u p . Fo r ex a m p le ,P P ', P S ', a n d P T ' e x h ib i t N H 2 w a g i n t h e r e g i o n s 7 6 0 - 7 8 0 c m - 1 , 7 7 9 - 7 9 9 c m - 1 , a n d 8 0 0 -813 c m - 1 , r e spec t iv e ly. I n ad d i t i o n , a wea k b an d a ss ig n ed to v C - N i s a l so a f f ect ed b y th e n a tu r eo f t h e a lk y l g r o u p . Fo r ex am p le , v C - N f o r PP ' , PS ', an d PT ' o ccu r i n t h e r eg io n s 1 0 4 3 -1 0 8 5 c m - 1 , 1 1 1 1 - 1 1 7 0 c m - 1 , a n d 1 1 8 5 - 1 2 6 5 c m - 1 , r e s p ec t iv e ly . B o t h N H 2 w a g a n d v C - Nin c r ea se in f r eq u en cy w i th in c r ea sed b r an c h in g o n th e 0 ~- ca rb o n a to m o f th e a lk y l g r o u p . Asa l r ead y n o ted h e r e , v sy m . NH 2 d ec r ea sed in f r eq u en cy w i th in c r ea sed b r an c h in g o n th e a lk y l 0~-ca r b o n a to m . T h e ap p a r en t r e a so n f o r th e d ec r ea se in f r eq u en cy o f v sy m . NH 2 i s t h a t w i thin c r ea sed b r an ch in g o n th e 0~-car bo n a to m m o r e e l ec t r o n s a r e r e l ea sed to t h e C - N g r o u p( in d u c t iv e a f fec t) . T h i s c au se s t h e N a to m to b eco m e m o r e b a s i c ; co n seq u en t ly , t h e N H 2 b o n d sa re w e a k e n e d c a u s i n g t h e v N H 2 m o d es to v ib ra t e a t l o wer f r eq u en c ie s . A l so, t h e i n d u c t iv e e f fec tin c r ea se s i n th e o r d e r P ', S ', an d T ' , an d th i s c au se s t h e C - N b o n d s t r en g th to in c r ea se in t h es a m e o r d er . C o n s e q u e n t ly , v C - N i n c re a s e s i n f re q u e n c y a s th e s t r e n g t h o f th e h y d r o g e n b o n dincreases . In add i t io n , the N H 2 wa g increase s in f re quen cy in the o rder P ', S ' , and T ' . Th is i sb ecau se i t t ak e s m o r e en e r g y f o r t h e two r e l a t iv e ly ch a r g ed N H 2 p r o to n s to wag ab o u t t h er e l a t iv e ly n eg a t iv e fr ee p a i r of e l ec t r o n s in t h e C - N p lan e a s t h e p r o to n s an d th e n i t r o g en a to mh av e in c r ea s in g ly r e l a t iv e o p p o s i t e e l ec t ri c a l ch a rg es . A s im i l a r ex p lan a t io n was p r e sen ted f o r t h ev O H , v C - O , O H t o r s i o n f o r a l k a n o l s ( s e e C h a p t e r 6 ) .


3/6

Variables in Data Interpreta t ion 145N H 2 B E N D I N G F O R A L K Y L A M I N E ST h e N H 2 b e n d i n g m o d e f o r t h e a l k y l a m i n e s w i t h p p t s t r u c t u r e o c c u r s i n t h e r e g i o n 1 5 9 9 -1629 c m -1 , wi t h P St i n t he r e g i on 1612 -1621 c m -1 , a nd wi t h P T t i n t he r e g i on 161 0-16 16 c m -1 ,a n d h a s w e a k t o w e a k - m e d i u m I R b a n d i n t e n s i ty i n t h e v a p o r p h a s e . T h e r e fo r e , t h e N H 2 b e n d i n gmo de f r e que nc i e s a re no t u se fu l fo r d i s t i ngu i sh i ng be t w e e n a l ky l a m i ne s w i t h P P t, P S , a nd P T ts t ruc t u re s . In t he l i qu i d it i s a s s i gne d i n t he r e g i on 159 0-16 27 c m -1 wi t h m e d i um i n t e ns i t y (3 ) .In c on t ra s t , NH 2 be nd fo r a ry l a mi ne s ( a n i l ine s ) oc c u r s a t h i ghe r f r e que nc y w i t h s t ron g IR ba n dintens i ty (3) . (See the next chapte r . )

R A M A N D A T A F O R P R I M A R Y A M I N E STa b l e 8 .2 l i s t s R a ma n da t a a nd a s s i gnme n t s fo r t he ne a t pha se fo r p r i ma ry a mi ne s .

I n t h e n e a t p h a s e , v a sy m . N H 2 a n d v s y m . N H 2 o c c u r i n t h e r e g i o n 3 3 6 7 - 3 3 7 9 c m - 1 a n d3 3 0 7 - 3 3 2 2 c m - 1 , r e spec t ive l y. In a l l c ase s , t he v sym. N H 2 mo de ha s m ore r e l a ti ve ba nd i n t e ns i t yt ha n t he va sym. NH 2 mo de s a s i nd i c a t e d by t he num be r i n pa re n t he s i s (2 ) .

I t is i n t e re s t i ng t o c om pa re t he va sym. N H 2 a nd vsym. NH 2 f re que nc i e s ob t a i ne d fo rbu t y l a m i ne (1 -a m i nobu t a ne ) i n t he va po r a n d l i qu i d pha se s : va sym. NH 2 (3411 c m -1 , va p .a nd 3376 c m -1 , l i q .) a nd vsym. NH 2 (3345 c m -1 , va p . a n d 3322 c m -1 , l i qu i d ) . Th i s c om pa r i so nshow s t ha t va sym. NH 2 a nd vsym. NH 2 oc c u r a t l owe r f r e que nc y i n t he l i qu i d ph a se by 35 a nd23 cm - 1 , re spec tive ly .

Two o f t he e xa mpl e s g i ve n i n Ta b l e 8 .2 c on t a i n a 4 -a mi noc yc l ohe xy l g roup , a nd bo t h e xh i b i ta v e r y s t r o n g R a m a n b a n d a t 7 8 4 c m - 1 , whi c h i s a s s i gne d t o t he c yc l ohe xy l b re a t h i ng mode .

C H E M I C A L R E A C T I O N S O F A L K Y L A M I N E S C O N T A I N I N GN H 2 O R N H G R O U P SThi s s e c t i on i s b ro ugh t t o t he r ea de r 's a t t e n t i on fo r ma t t e r s o f s a fe t y a nd be c a use i t c a n c a usec onfus i on whe n i n t e rp re t i ng spe c t r a l da t a .

F ro m e xp e r i e nc e i t ha s be e n no t e d t ha t he a t ge ne ra t e d f rom t he c he mi c a l r e a c t i on o f al i pha t i cp r i m a ry o r s e c o nda ry a mi ne s w i t h C S 2 c a n c a use t he e n t i r e c o n t e n t o f the vo l um e t r i c f l ask t oblow out of i t s mouth . This can cause an in jury , or poss ib ly a f i re , because CS2 has a lowflashpoint .

The se c he mi c a l r e a c t i ons oc c u r a s fo l l ows :S

I I2R-NH 2+CS2 -> R -N-C-S" N* H3-R

IHSI I2(R-)2NH + CS2 -~ (R-)2N-C-S" +NH (-R)2


4/6

1 4 6 Al iphati c Am inesA s w e ll , if e x p o s e d t o a ir f o r a p e r i o d o f t im e t h e s e s a m e a l k y l a m i n e s c a n u n d e r g o c o m p a r a b l er e a c t i o n s w i t h C O 2 ( r e p la c e C S 2 w i t h C O 2 ) . I n a d d i t io n , a l k y l a m i n e s c a n r e a c t s l o w l y w i t hs o l v e n t s s u c h a s CC1 4 , CH C1 3, a n d CH 2C1 2, a n d t h i s c a n c a u s e p r o b l e m s i n s p e c i f i c a l l yi d e n t i f y i n g t h e o r i g i n a l s a mp l e .

S E C O N D A R Y A L I P H A T I C A M I N E ST h e N - H s t r e t c h i n g b a n d f o r c o m p o u n d s o f f o r m ( R - - ) 2 N H i s w e a k , a n d i s n o t r e a d il y d e t e c t e di n c o m p o u n d s w h o s e I R s p e c t r a h a v e b e e n r e c o r d e d i n t h e v a p o r p h a s e ( 1 ) . H o w e v e r , N - H w a gh a s s t r o n g I R b a n d i n t e n s i ty w i t h h a l f b a n d w i d t h s v a r y i n g b e t w e e n 5 0 a n d 1 0 0 c m - 1 a n d o c c u r si n t h e r e g i o n 6 8 6 - 7 5 0 c m - 1 i n t h e v a p o r p h a s e . T h u s , i t o c c u r s a t l o w e r f r e q u e n c y t h a n N H 2w a g . I n t h e l iq u i d , t h e w e a k I R b a n d o c c u r s i n t h e r e g i o n 3 3 2 0 - 3 2 8 0 c m - 1 a n d i n d i l u te s o l u t i o ni n t h e r e g i o n 3 3 1 0 - 3 3 6 0 c m - 1 ( 3 ).

D i a l k y l a m i n e s w i t h S PIP I s t r u c t u r e e x h i b i t N H w a g i n t h e r e g i o n 6 9 9 - 7 1 5 c m - 1 , w i t h S P ISs t r u c t u r e n e a r " -,6 86 c m - 1 . T h e s e d a t a s u g g e s t t h a t N H w a g d e c r e a s e s i n f r e q u e n c y i n t h e o r d e rSS~S~, SPa S , a n d SPIP t, w h i c h i s t h e o p p o s i t e o r d e r f o r t h e p r i m a r y a l k y l a mi n e s ( s e e t h e p r e c e d i n gma t e r i a l s h e r e ) .

I n t h e d i a lk y l a m i n e s e r ie s w i t h S P 'P ~ s t r u c t u r e a b a n d a s s i g n e d a s v N ( - C ) 2 o c c u r s i n t h er e g i o n 1 1 3 2 - 1 1 5 1 c m - 1 ( 1 ).

R E F E R E N C E S1. Nyq uist, R. A. (1984). The Interpretation of Vapor-Phase Infrared Spectra: Group Frequency Data, Philadelphia: SadtlerResearch Laboratories, Division of Bio-Rad Laboratories, Inc.2. Ram an D ata from the Sadtler Research Laboratories, Philadelphia: Division of Bio-Rad Laboratories, Inc.3. Lin-V ien, D., Co lthup , N. B., Fateley, W. G., and G rasselli, J. G . (1 991 ). The Handbo ok of Infrared and Raman Char-

acteristic Frequencies of Organic Molecules, San Diego: Academic Press.


5/6

V a r i a b le s i n D a t a I n t e r p r e t a t i o n 14 7T A BL E 8 .1 I R v a p o r - p h a s e d a ta a n d a s s i g n m e n t s f o r p r i m a r y a m i n e s

(A) INH2 (A)[NH 2a.CH 3 a .CH 2 s .CH 3 s .CH 2 CH 2 s .CH 3 NH 2 wag] wag]

Amine s t r. s t r. s t r. s tr . bend bend wag (A)[s .CH 2 s t r .l (A)[CH 2 bend]

Methyl 2960(0 .640)EthylPropyl

(1 .230)Buty l 2940

(1 .250)Hepty l 2970 2940

(0 .700) (1 .250)Octy l 2970 2930

(0 .462) (1 .250)Nonyl 2970 2930

(0 .460) (1 .250)Decyl 2970 2935

(0 .290) (1 .250)Undecyl 2970 2935

(0 .410) (1 .210)Tridecyl 2935

(1 .250)Tetradecyl 2938

(1 .250)Pentadecyl 2930

(1 .250)Octadecyl 2970 2935

(0 .040) (1 .250)Nonadecyl 2930

(1 .250)

2898 778(0 .600) (0 .784)2965 2922 2870 1456 1398 772 1 .69

(1 .240) (0 .940) (0 .640) (0 .164) (0 .280) (1 .087)2978 2880 1465 1387 764 0 .93

(0 .679) (0 .135) (0 .129) (0 .630)2880 1465 1387 779 1 .07

(0 .621) (0 .120) (0 .111) (0 .664)2868 1468 1377 770 0 .49

(0 .510) (0 .130) (0 .080) (0 .248)2964 1465 1385 771 0 .37

(0 .510) (0 .091) (0 .050) (0 .190)2864 1466 1388 775 0 .36

(0 .530) (0 .100) (0 .066) (0 .189)2864 1466 1385 780 0 .32

(0 .380) (0 .080) (0 .035) (0 .120)2864 1465 1385 775 0.23

(0 .570) (0 .100) (0 .050) (0 .131)2864 1460 1389 775 O. 16

(0 .310) (0 .050) (0 .020) (0 .050)2864 1460 1385 770 0 .19

(0 .310) (0 .058) (0 .050) (0 .060)2860 1460 1385 770 0 .13

(0 .310) (0 .059) (0 .011) (0 .040)2962 1465 1385 775 0.11

(0 .310) (0 .045) (0 .005) (0 .035)2860 1460 1385 775 0 .11

(0 .400) (0 .089) (0 .005) (0 .044)Cyclopropyl 3100

(0 .220)Cyclopenty l 2968

(1 .250)2935

(1 .250)Cyclohepty l 2930

(1 .250)Cyclooc ty l 2932

(1 .150)

3010 1455 755 4 .03(0 .250) (0 .140) (1 .230)

2884 1459 779 0 .53(0 .420) (0 .061) (0 .223)

2864 1458 770 0 .41(0 .420) (0 .130) (0 .170)

2860 1460 784 0 .47(0 .320) (0 .100) (0 .151)

2868 1459 785 0 .31(0 .199) (0 .069) (0 .060)

6.634.675.531.9

2.091 . 8 9

1.511.111 .0 1

1.110 .680.770.49

8.793.661.421.510 .87


6/6

1 4 8 Aliphatic AminesTABLE 8.2 Raman data and assignments for primary amines

bis-(4-Amino- Hexa- 2-Aminoethyl 3-Methoxy-1-Amino- cyclohexyl) Ethoxyethyl methylene methyl propylbutane methane amine diamine ether amine

4,4'-bis(p-Amino-cyclo-

hexyl) methane Assignment3376(1)3322(3)2963(5)2938(7)2875(4)

1444(7)

3311(1)

1441(5)784(9)

3379(1) 3367(1) 3379(1) 3377(2) 3367(0)3322(3) 3307(3) 3322(3) 3319(5) 3312(1)2977(5) 2985(5)2934(9) 2950(6) 2929(7) 2931(2)2899(1)2870(5) 2868(4)

2853(2) 2823(4) 2826(6) 2846(3)2811(5)

2797(2) 2723(2) 2755(3)1640(1) 1597(1)

1459(6) 1440(9) 1453(9) 1450(9) 1441(5)784(9)

a.NH 2s.NH 2a.CH 3 str.a.CH 2 str.a.CH 2 str.s.CH 2 str.s.CH 2 str.C.T.

C.T.NH 2 bendCH 2 bendRing breathing

aliphatic amines in physics

Documents